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• Ubuntu 13.04 can only work in recovery mode

  - by zhangyangyu

  I have just updated my 12.10 to 13.04. Everything is updated. But I can only boot to a black screen. I mean after the GRUB interface and purple screen. And I can hear the voice of the password interface. But it is only the black screen. It all works OK in 12.10. But it can work in the recovery mode. I mean go into the recovery mode and choose resume. And then everything is OK. But when loading kernel, the screen is dirty. I don't know why and I have Googled a lot. But no resolutions works. My graphics card is Intel GMA HD 4000, tested as VESA: Intel® Sandybridge/Ivybridge Graphics. I have been trapped in this for a whole day. I do need help. Hope someone can help me. By the way, the kernel is 3.8.0-19 if it helps.

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• Hyper-V: determine the guest's name given the GUID

  - by syneticon-dj

  How would I go about determining the guest's name given its GUID or vice-versa, preferably with only the Hyper-V/Server Core stock install at hands? Rationale: I am in favor of having a repository of dirty tricks to revert to when in great need. To immediately quiesce all (storage) operations of a VM guest without losing the state, I used to run kill 17 <all VM's virtual processes> (signaling SIGSTOP) and resumed afterwards using kill 19 <all VM's virtual processes> (signaling SIGCONT) in ESXi/vSphere shell. I tried the same technique with Hyper-V using Process Explorer's "Suspend" functionality on the vmwp.exe processes and it seemed to work. I have yet to find a way for easily identifying the processes to suspend, though - the vmwp command line is only listing a GUID.

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• How do I edit files in the console when connecting to windows 7 via ssh?

  - by Alex Waters

  I am using tunnelier client and server to connect to a windows machine. I can get in and have access to all of the files on the computer. I have vim installed on that windows machine, but I can't seem to edit anything via the DOS command line. I also tried editing in notepad, but nothing happens when I enter the command. I think this might be the part where DOS doesn't behave like bash. Would I need to setup cygwin / openssh to accomplish this? (boo, tunnelier is so easy) Thanks! p.s. I know I could just use sftp and edit files that way, but it feels dirty.

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• Replacement for Picasa [closed]

  - by January

  Possible Duplicate: What is the best alternative to Picasa? I use Picasa not because it is a great photo manager -- it's not, the manager is "sort of OK" for my taste. However, it combines a passable photo manager with a good "quick and dirty" image editor. It has the basic functions like cropping, resizing, contrast and color adjustment, and the one great feature -- "I'm feeling lucky" button, that works in 90% of the cases. Also, from time to time, I use one or two of the effects (like saturation or sharpening). GIMP is great and I use it on a regular basis, but in most cases I just want to go quickly through the photographs of my kids birthday and make them more presentable without much fuss. I'm looking for a native, open source replacement, something that would not miss the editing capabilities of Picasa and would allow me to quickly go through a collection of photographs and make basic edits. A function similar to "I'm feeling lucky" (automatic adjustment of contrast, color and brightness) would be most welcome. EDIT: Yes, I have already tried a number of alternatives, if it is necessary I can produce a detailed list here, along with the problems I found. I'm posting that question because I hope to see a new name.

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• How do you install a new build controller in TFS?

  - by JL.

  I am not looking for detailed instructions, I just want the quick and dirty overview. We have an existing TFS infrastructure, I am looking to install a new build controller for 1 team project. Do I need to create a new VM and install TFS (configure as controller) and then link it from the VM to the main TFS instance? OR Do I need to create the new VM, install TFS (configure as controller) and then - From the main TFS admin console on the main TFS server - add the new controller? Thanks in advance?

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• Positioned element adding to total div height [migrated]

  - by Max

  I have a 800 x 600 rotatable image with forward and back buttons repositioned to the sides. The height of the div is suppose to be 600px, but the actual height of the div was pushed to 690, including the height of the button image. And the div was blocking a row of clickable menu on top. So I made the div height to 518px and moved top -75px to get the real dimension I want. But I feel dirty doing this... Is there a correct way to do this? Or is this workaround more or less correct? Below is the code. Thanks! <div class="Content Wide" id="LayoutColumn1"> <div style=" width: 980px; height: 518px; display: block; position: relative; float: left;"> <a href="#" onClick="prev();"><img src="/template/img/next_button.png" style="position: relative; top: 200px; left: 5px; z-index: 2;"></a> <a href="/chef-special/" id="mainLink"><img src="/template/img/chef_special_large.png" id="main" style="margin: 0 0 0 50px; position: relative; float: left; top: -75px; z-index: 1;"></a> <a href="#" onClick="next();"><img src="/template/img/next_button.png" style="position: relative; top: 200px; left: 787px; z-index: 2;"></a> </div> </div>

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• Const references when dereferencing iterator on set, starting from Visual Studio 2010

  - by Patrick

  Starting from Visual Studio 2010, iterating over a set seems to return an iterator that dereferences the data as 'const data' instead of non-const. The following code is an example of something that does compile on Visual Studio 2005, but not on 2010 (this is an artificial example, but clearly illustrates the problem we found on our own code). In this example, I have a class that stores a position together with a temperature. I define comparison operators (not all them, just enough to illustrate the problem) that only use the position, not the temperature. The point is that for me two instances are identical if the position is identical; I don't care about the temperature. #include <set> class DataPoint { public: DataPoint (int x, int y) : m_x(x), m_y(y), m_temperature(0) {} void setTemperature(double t) {m_temperature = t;} bool operator<(const DataPoint& rhs) const { if (m_x==rhs.m_x) return m_y<rhs.m_y; else return m_x<rhs.m_x; } bool operator==(const DataPoint& rhs) const { if (m_x!=rhs.m_x) return false; if (m_y!=rhs.m_y) return false; return true; } private: int m_x; int m_y; double m_temperature; }; typedef std::set<DataPoint> DataPointCollection; void main(void) { DataPointCollection points; points.insert (DataPoint(1,1)); points.insert (DataPoint(1,1)); points.insert (DataPoint(1,2)); points.insert (DataPoint(1,3)); points.insert (DataPoint(1,1)); for (DataPointCollection::iterator it=points.begin();it!=points.end();++it) { DataPoint &point = *it; point.setTemperature(10); } } In the main routine I have a set to which I add some points. To check the correctness of the comparison operator, I add data points with the same position multiple times. When writing the contents of the set, I can clearly see there are only 3 points in the set. The for-loop loops over the set, and sets the temperature. Logically this is allowed, since the temperature is not used in the comparison operators. This code compiles correctly in Visual Studio 2005, but gives compilation errors in Visual Studio 2010 on the following line (in the for-loop): DataPoint &point = *it; The error given is that it can't assign a "const DataPoint" to a [non-const] "DataPoint &". It seems that you have no decent (= non-dirty) way of writing this code in VS2010 if you have a comparison operator that only compares parts of the data members. Possible solutions are: Adding a const-cast to the line where it gives an error Making temperature mutable and making setTemperature a const method But to me both solutions seem rather 'dirty'. It looks like the C++ standards committee overlooked this situation. Or not? What are clean solutions to solve this problem? Did some of you encounter this same problem and how did you solve it? Patrick

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• Forms bound to updateable ADO recordsets are not updateable when the source includes a JOIN

  - by Art

  I'm developing an application in Access 2007. It uses an .accdb front end connecting to an SQL Server 2005 backend. I use forms that are bound to ADO recordsets at runtime. For the sake of efficiency, the recordsets usually contain only one record, and are queried out on the server: Public Sub SetUpFormRecordset(cn As ADODB.Connection, rstIn As ADODB.Recordset, rstSource As String) Dim cmd As ADODB.Command Dim I As Long Set cmd = New ADODB.Command cn.Errors.Clear ' Recordsets based on command object Execute method are Read Only! With cmd Set .ActiveConnection = cn .CommandType = adCmdText .CommandText = rstSource End With With rstIn .CursorType = adOpenKeyset .LockType = adLockPessimistic 'Check the locktype after opening; optimistic locking is worthless on a bound End With ' form, and ADO might open optimistically without firing an error! rstIn.Open cmd, , adOpenKeyset, adLockPessimistic 'This should run the query on the server and return an updatable recordset With cn If .Errors.Count <> 0 Then For Each errADO In .Errors Call HandleADOErrors(.Errors(I)) I = I + 1 Next errADO End If End With End Sub rstSource (the string containg the TSQL on which the recordset is based) is assembled by the calling routine, in this case from the Open event of the form being bound: Private Sub Form_Open(Cancel As Integer) Dim rst As ADODB.Recordset Dim strSource As String, DefaultSource as String Dim lngID As Long lngID = Forms!MyParent.CurrentID strSource = "SELECT TOP (100) PERCENT dbo.Customers.CustomerID, dbo.Customers.LegacyID, dbo.Customers.Active, dbo.Customers.TypeID, dbo.Customers.Category, " & _ "dbo.Customers.Source, dbo.Customers.CustomerName, dbo.Customers.CustAddrID, dbo.Customers.Email, dbo.Customers.TaxExempt, dbo.Customers.SalesTaxCode, " & _ "dbo.Customers.SalesTax2Code, dbo.Customers.CreditLimit, dbo.Customers.CreationDate, dbo.Customers.FirstOrder, dbo.Customers.LastOrder, " & _ "dbo.Customers.nOrders, dbo.Customers.Concurrency, dbo.Customers.LegacyLN, dbo.Addresses.AddrType, dbo.Addresses.AddrLine1, dbo.Addresses.AddrLine2, " & _ "dbo.Addresses.City, dbo.Addresses.State, dbo.Addresses.Country, dbo.Addresses.PostalCode, dbo.Addresses.PhoneLandline, dbo.Addresses.Concurrency " & _ "FROM dbo.Customers INNER JOIN " & _ "dbo.Addresses ON dbo.Customers.CustAddrID = dbo.Addresses.AddrID " strSource = strSource & "WHERE dbo.Customers.CustomerID= " & lngID With Me 'Default is Set up for editing one record If Not Nz(.RecordSource, vbNullString) = vbNullString Then If .Dirty Then .Dirty = False 'Save any changes on the form .RecordSource = vbNullString End If If rst Is Nothing Then 'Might not be first time through DefaultSource = .RecordSource Else rst.Close Set rst = Nothing End If End With Set rst = New ADODB.Recordset Call setupformrecordset(dbconn, rst, strSource) 'dbconn is a global variable With Me Set .Recordset = rst End With End Sub The recordset that is returned from setupformrecordset is fully updateable, and its .Supports property shows this. It can be edited and updated in code. The entire form, however, is read only, even though it's .AllowEdits and .AllowAdditions properties are both true. Even the fields from the right hand side (the 'many' side) cannot be edited. Removing the INNER JOIN clause from the TSQL (restricting strSource to one table) makes the form fully editable. I've verified that the TSQL includes priimary key fields from both tables, and each table includes a timestamp field for concurrency. I tried changing the .CursorType and .CursorLocation properties of the recordset to no avail. What am I doing wrong?

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• Differences Between NHibernate and Entity Framework

  - by Ricardo Peres

  Introduction NHibernate and Entity Framework are two of the most popular O/RM frameworks on the .NET world. Although they share some functionality, there are some aspects on which they are quite different. This post will describe this differences and will hopefully help you get started with the one you know less. Mind you, this is a personal selection of features to compare, it is by no way an exhaustive list. History First, a bit of history. NHibernate is an open-source project that was first ported from Java’s venerable Hibernate framework, one of the first O/RM frameworks, but nowadays it is not tied to it, for example, it has .NET specific features, and has evolved in different ways from those of its Java counterpart. Current version is 3.3, with 3.4 on the horizon. It currently targets .NET 3.5, but can be used as well in .NET 4, it only makes no use of any of its specific functionality. You can find its home page at NHForge. Entity Framework 1 came out with .NET 3.5 and is now on its second major version, despite being version 4. Code First sits on top of it and but came separately and will also continue to be released out of line with major .NET distributions. It is currently on version 4.3.1 and version 5 will be released together with .NET Framework 4.5. All versions will target the current version of .NET, at the time of their release. Its home location is located at MSDN. Architecture In NHibernate, there is a separation between the Unit of Work and the configuration and model instances. You start off by creating a Configuration object, where you specify all global NHibernate settings such as the database and dialect to use, the batch sizes, the mappings, etc, then you build an ISessionFactory from it. The ISessionFactory holds model and metadata that is tied to a particular database and to the settings that came from the Configuration object, and, there will typically be only one instance of each in a process. Finally, you create instances of ISession from the ISessionFactory, which is the NHibernate representation of the Unit of Work and Identity Map. This is a lightweight object, it basically opens and closes a database connection as required and keeps track of the entities associated with it. ISession objects are cheap to create and dispose, because all of the model complexity is stored in the ISessionFactory and Configuration objects. As for Entity Framework, the ObjectContext/DbContext holds the configuration, model and acts as the Unit of Work, holding references to all of the known entity instances. This class is therefore not lightweight as its NHibernate counterpart and it is not uncommon to see examples where an instance is cached on a field. Mappings Both NHibernate and Entity Framework (Code First) support the use of POCOs to represent entities, no base classes are required (or even possible, in the case of NHibernate). As for mapping to and from the database, NHibernate supports three types of mappings: XML-based, which have the advantage of not tying the entity classes to a particular O/RM; the XML files can be deployed as files on the file system or as embedded resources in an assembly; Attribute-based, for keeping both the entities and database details on the same place at the expense of polluting the entity classes with NHibernate-specific attributes; Strongly-typed code-based, which allows dynamic creation of the model and strongly typing it, so that if, for example, a property name changes, the mapping will also be updated. Entity Framework can use: Attribute-based (although attributes cannot express all of the available possibilities – for example, cascading); Strongly-typed code mappings. Database Support With NHibernate you can use mostly any database you want, including: SQL Server; SQL Server Compact; SQL Server Azure; Oracle; DB2; PostgreSQL; MySQL; Sybase Adaptive Server/SQL Anywhere; Firebird; SQLLite; Informix; Any through OLE DB; Any through ODBC. Out of the box, Entity Framework only supports SQL Server, but a number of providers exist, both free and commercial, for some of the most used databases, such as Oracle and MySQL. See a list here. Inheritance Strategies Both NHibernate and Entity Framework support the three canonical inheritance strategies: Table Per Type Hierarchy (Single Table Inheritance), Table Per Type (Class Table Inheritance) and Table Per Concrete Type (Concrete Table Inheritance). Associations Regarding associations, both support one to one, one to many and many to many. However, NHibernate offers far more collection types: Bags of entities or values: unordered, possibly with duplicates; Lists of entities or values: ordered, indexed by a number column; Maps of entities or values: indexed by either an entity or any value; Sets of entities or values: unordered, no duplicates; Arrays of entities or values: indexed, immutable. Querying NHibernate exposes several querying APIs: LINQ is probably the most used nowadays, and really does not need to be introduced; Hibernate Query Language (HQL) is a database-agnostic, object-oriented SQL-alike language that exists since NHibernate’s creation and still offers the most advanced querying possibilities; well suited for dynamic queries, even if using string concatenation; Criteria API is an implementation of the Query Object pattern where you create a semi-abstract conceptual representation of the query you wish to execute by means of a class model; also a good choice for dynamic querying; Query Over offers a similar API to Criteria, but using strongly-typed LINQ expressions instead of strings; for this, although more refactor-friendlier that Criteria, it is also less suited for dynamic queries; SQL, including stored procedures, can also be used; Integration with Lucene.NET indexer is available. As for Entity Framework: LINQ to Entities is fully supported, and its implementation is considered very complete; it is the API of choice for most developers; Entity-SQL, HQL’s counterpart, is also an object-oriented, database-independent querying language that can be used for dynamic queries; SQL, of course, is also supported. Caching Both NHibernate and Entity Framework, of course, feature first-level cache. NHibernate also supports a second-level cache, that can be used among multiple ISessionFactorys, even in different processes/machines: Hashtable (in-memory); SysCache (uses ASP.NET as the cache provider); SysCache2 (same as above but with support for SQL Server SQL Dependencies); Prevalence; SharedCache; Memcached; Redis; NCache; Appfabric Caching. Out of the box, Entity Framework does not have any second-level cache mechanism, however, there are some public samples that show how we can add this. ID Generators NHibernate supports different ID generation strategies, coming from the database and otherwise: Identity (for SQL Server, MySQL, and databases who support identity columns); Sequence (for Oracle, PostgreSQL, and others who support sequences); Trigger-based; HiLo; Sequence HiLo (for databases that support sequences); Several GUID flavors, both in GUID as well as in string format; Increment (for single-user uses); Assigned (must know what you’re doing); Sequence-style (either uses an actual sequence or a single-column table); Table of ids; Pooled (similar to HiLo but stores high values in a table); Native (uses whatever mechanism the current database supports, identity or sequence). Entity Framework only supports: Identity generation; GUIDs; Assigned values. Properties NHibernate supports properties of entity types (one to one or many to one), collections (one to many or many to many) as well as scalars and enumerations. It offers a mechanism for having complex property types generated from the database, which even include support for querying. It also supports properties originated from SQL formulas. Entity Framework only supports scalars, entity types and collections. Enumerations support will come in the next version. Events and Interception NHibernate has a very rich event model, that exposes more than 20 events, either for synchronous pre-execution or asynchronous post-execution, including: Pre/Post-Load; Pre/Post-Delete; Pre/Post-Insert; Pre/Post-Update; Pre/Post-Flush. It also features interception of class instancing and SQL generation. As for Entity Framework, only two events exist: ObjectMaterialized (after loading an entity from the database); SavingChanges (before saving changes, which include deleting, inserting and updating). Tracking Changes For NHibernate as well as Entity Framework, all changes are tracked by their respective Unit of Work implementation. Entities can be attached and detached to it, Entity Framework does, however, also support self-tracking entities. Optimistic Concurrency Control NHibernate supports all of the imaginable scenarios: SQL Server’s ROWVERSION; Oracle’s ORA_ROWSCN; A column containing date and time; A column containing a version number; All/dirty columns comparison. Entity Framework is more focused on Entity Framework, so it only supports: SQL Server’s ROWVERSION; Comparing all/some columns. Batching NHibernate has full support for insertion batching, but only if the ID generator in use is not database-based (for example, it cannot be used with Identity), whereas Entity Framework has no batching at all. Cascading Both support cascading for collections and associations: when an entity is deleted, their conceptual children are also deleted. NHibernate also offers the possibility to set the foreign key column on children to NULL instead of removing them. Flushing Changes NHibernate’s ISession has a FlushMode property that can have the following values: Auto: changes are sent to the database when necessary, for example, if there are dirty instances of an entity type, and a query is performed against this entity type, or if the ISession is being disposed; Commit: changes are sent when committing the current transaction; Never: changes are only sent when explicitly calling Flush(). As for Entity Framework, changes have to be explicitly sent through a call to AcceptAllChanges()/SaveChanges(). Lazy Loading NHibernate supports lazy loading for Associated entities (one to one, many to one); Collections (one to many, many to many); Scalar properties (thing of BLOBs or CLOBs). Entity Framework only supports lazy loading for: Associated entities; Collections. Generating and Updating the Database Both NHibernate and Entity Framework Code First (with the Migrations API) allow creating the database model from the mapping and updating it if the mapping changes. Extensibility As you can guess, NHibernate is far more extensible than Entity Framework. Basically, everything can be extended, from ID generation, to LINQ to SQL transformation, HQL native SQL support, custom column types, custom association collections, SQL generation, supported databases, etc. With Entity Framework your options are more limited, at least, because practically no information exists as to what can be extended/changed. It features a provider model that can be extended to support any database. Integration With Other Microsoft APIs and Tools When it comes to integration with Microsoft technologies, it will come as no surprise that Entity Framework offers the best support. For example, the following technologies are fully supported: ASP.NET (through the EntityDataSource); ASP.NET Dynamic Data; WCF Data Services; WCF RIA Services; Visual Studio (through the integrated designer). Documentation This is another point where Entity Framework is superior: NHibernate lacks, for starters, an up to date API reference synchronized with its current version. It does have a community mailing list, blogs and wikis, although not much used. Entity Framework has a number of resources on MSDN and, of course, several forums and discussion groups exist. Conclusion Like I said, this is a personal list. I may come as a surprise to some that Entity Framework is so behind NHibernate in so many aspects, but it is true that NHibernate is much older and, due to its open-source nature, is not tied to product-specific timeframes and can thus evolve much more rapidly. I do like both, and I chose whichever is best for the job I have at hands. I am looking forward to the changes in EF5 which will add significant value to an already interesting product. So, what do you think? Did I forget anything important or is there anything else worth talking about? Looking forward for your comments!

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• Inequality joins, Asynchronous transformations and Lookups : SSIS

  - by jamiet

  It is pretty much accepted by SQL Server Integration Services (SSIS) developers that synchronous transformations are generally quicker than asynchronous transformations (for a description of synchronous and asynchronous transformations go read Asynchronous and synchronous data flow components). Notice I said “generally” and not “always”; there are circumstances where using asynchronous transformations can be beneficial and in this blog post I’ll demonstrate such a scenario, one that is pretty common when building data warehouses. Imagine I have a [Customer] dimension table that manages information about all of my customers as a slowly-changing dimension. If that is a type 2 slowly changing dimension then you will likely have multiple rows per customer in that table. Furthermore you might also have datetime fields that indicate the effective time period of each member record. Here is such a table that contains data for four dimension members {Terry, Max, Henry, Horace}: Notice that we have multiple records per customer and that the [SCDStartDate] of a record is equivalent to the [SCDEndDate] of the record that preceded it (if there was one). (Note that I am on record as saying I am not a fan of this technique of storing an [SCDEndDate] but for the purposes of clarity I have included it here.) Anyway, the idea here is that we will have some incoming data containing [CustomerName] & [EffectiveDate] and we need to use those values to lookup [Customer].[CustomerId]. The logic will be: Lookup a [CustomerId] WHERE [CustomerName]=[CustomerName] AND [SCDStartDate] <= [EffectiveDate] AND [EffectiveDate] <= [SCDEndDate] The conventional approach to this would be to use a full cached lookup but that isn’t an option here because we are using inequality conditions. The obvious next step then is to use a non-cached lookup which enables us to change the SQL statement to use inequality operators: Let’s take a look at the dataflow: Notice these are all synchronous components. This approach works just fine however it does have the limitation that it has to issue a SQL statement against your lookup set for every row thus we can expect the execution time of our dataflow to increase linearly in line with the number of rows in our dataflow; that’s not good. OK, that’s the obvious method. Let’s now look at a different way of achieving this using an asynchronous Merge Join transform coupled with a Conditional Split. I’ve shown it post-execution so that I can include the row counts which help to illustrate what is going on here: Notice that there are more rows output from our Merge Join component than on the input. That is because we are joining on [CustomerName] and, as we know, we have multiple records per [CustomerName] in our lookup set. Notice also that there are two asynchronous components in here (the Sort and the Merge Join). I have embedded a video below that compares the execution times for each of these two methods. The video is just over 8minutes long. View on Vimeo  For those that can’t be bothered watching the video I’ll tell you the results here. The dataflow that used the Lookup transform took 36 seconds whereas the dataflow that used the Merge Join took less than two seconds. An illustration in case it is needed: Pretty conclusive proof that in some scenarios it may be quicker to use an asynchronous component than a synchronous one. Your mileage may of course vary. The scenario outlined here is analogous to performance tuning procedural SQL that uses cursors. It is common to eliminate cursors by converting them to set-based operations and that is effectively what we have done here. Our non-cached lookup is performing a discrete operation for every single row of data, exactly like a cursor does. By eliminating this cursor-in-disguise we have dramatically sped up our dataflow. I hope all of that proves useful. You can download the package that I demonstrated in the video from my SkyDrive at http://cid-550f681dad532637.skydrive.live.com/self.aspx/Public/BlogShare/20100514/20100514%20Lookups%20and%20Merge%20Joins.zip Comments are welcome as always. @Jamiet Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• CodePlex Daily Summary for Wednesday, May 14, 2014

  CodePlex Daily Summary for Wednesday, May 14, 2014Popular ReleasesQuickMon: Version 3.10: Adding the ability to see 'history' of Collector states (including details of errors or warnings at that time). The history size is configurable (default is switched off) and the Windows Service completely ignores keeping history (no UI or user to access it anyway). The Collector stats window now displays this history plus multiple collector stats windows can be opened at the same time. Additionally fixed a bug in the event log collector that reported an 'Error' state when an 'out of bounds' ...xFunc: xFunc 2.15.4: Fixed bug in Processor.csTFS Planning and Disaster Recovery Avoidance Guide: v1.4.BETA - TFS, DR and Azure IaaS Planning Guides: Welcome to the TFS Planning and DR Avoidance Guidance What is new? A new crisper, more compact style, which is easier to consume on multiple devices without sacrificing any content. Also included are the new TFS on Azure IaaS guide and supplementary guides. Note Capacity planning workbook and posters are included in the Everything Zip package. Quality-Bar Detail Documentation has been reviewed by Visual Studio ALM Rangers Documentation has been through an independent technical review ...WinAudit: WinAudit Freeware v3.0: WinAudit.exe v3.0 MD5: 88750CCF49FF7418199B2645755830FA Known Issues: 1. Report creation can be very slow when right-to-left (Hebrew) characters are present. 2. Emsisoft Anti-Malware may stop and/or quarantine WinAudit. This happens when WinAudit attempts to obtain a list if running programmes. You will need to set an exception rule in Emsisoft to allow WinAudit to run.MVCwCMS - ASP.NET MVC CMS: MVCwCMS 2.2.2: Updated CKFinder config. For the installation instructions visit the documentation page: https://mvcwcms.codeplex.com/documentationTerraMap (Terraria World Map Viewer): TerraMap 1.0.4: Added support for the new Terraria v1.2.4 update. New items, walls, and tiles Fixed Issue 35206: Hightlight/Find doesn't work for Demon Altars Fixed finding Demon Hearts/Shadow Orbs Added ability to find Enchanted Swords (in the stone) and Water Bolt books Fixed installer not uninstalling older versions The setup file will make sure .NET 4 is installed, install TerraMap, create desktop and start menu shortcuts, add a .wld file association, and launch TerraMap. If you prefer the zip ...WPF Localization Extension: v2.2.1: Issue #9277 Issue #9292 Issue #9311 Issue #9312 Issue #9313 Issue #9314CtrlAltStudio Viewer: CtrlAltStudio Viewer 1.2.1.41167 Release: This release of the CtrlAltStudio Viewer includes the following significant features: Oculus Rift support. Stereoscopic 3D display support. Variable walking / flying speed. Xbox 360 Controller support. Kinect for Windows support. Based on Firestorm viewer 4.6.5 codebase. For more details, see the release notes linked to below. Release notes: http://ctrlaltstudio.com/viewer/release-notes/1-2-1-41167-release Support info: http://ctrlaltstudio.com/viewer/support Privacy policy: http:/...ExtJS based ASP.NET Controls: FineUI v4.0.6: FineUI（???） ?? ExtJS ??? ASP.NET ??? FineUI??? ?? No JavaScript，No CSS，No UpdatePanel，No ViewState，No WebServices ??????? ?????? IE 8.0+、Chrome、Firefox、Opera、Safari ???? Apache License v2.0 ?：ExtJS ?? GPL v3 ?????(http://www.sencha.com/license) ???? ??：http://fineui.com/ ??：http://fineui.com/bbs/ ??：http://fineui.com/demo/ ??：http://fineui.com/doc/ ??：http://fineui.codeplex.com/ FineUI ???? ExtJS ????????，???? ExtJS ?，?????： 1. ????? FineUI ? ExtJS ? http://fineui.com/bbs/forum.ph...Office App Model Samples: Office App Model Samples v2.0: Office App Model Samples v2.0Readable Passphrase Generator: KeePass Plugin 0.13.0: Version 0.13.0 Added "mutators" which add uppercase and numbers to passphrases (to help complying with upper, lower, number complexity rules). Additional API methods which help consuming the generator from 3rd party c# projects. 13,160 words in the default dictionary (~600 more than previous release).CS-Script for Notepad++ (C# intellisense and code execution): Release v1.0.25.0: Release v1.0.25.0 MemberInfo/MethodInfo popup is now positioned properly to fit the screen In MethodInfo popup method signatures are word-wrapped Implemented Debug text value visualizer Pining sub-values from Watch PanelWrapper for the PAYMILL API: Paymill API Wrapper: Add Description in PreauthorizationHow to develop an autodialer / predictive dialer in C#: VoIP AutoDialer in C Sharp: This is the downloadable source code for this example project that is intended to help you in developing your own VoIP autodialer application in C#.R.NET: R.NET 1.5.12: R.NET 1.5.12 is a beta release towards R.NET 1.6. You are encouraged to use 1.5.12 now and give feedback. See the documentation for setup and usage instructions. Main changes for R.NET 1.5.12: The C stack limit was not disabled on Windows. For reasons possibly peculiar to R, this means that non-concurrent access to R from multiple threads was not stable. This is now fixed, with the fix validated with a unit test. Thanks to Odugen, skyguy94, and previously others (evolvedmicrobe, tomasp) fo...CTI Text Encryption: CTI Text Encryption 5.2: Change log: 5.2 - Remove Cut button. - Fixed Reset All button does not reset encrypted text column. - Switch button location between Copy and Paste. - Enable users to use local fonts to display characters of their language correctly. (A font settings file will be saved at the same folder of this program.) 5.1 - Improve encryption process. - Minor UI update. - Version 5.1 is not compatible with older version. 5.0 - Improve encryption algorithm. - Simply inner non-encryption related mec...SEToolbox: SEToolbox 01.029.006 Release 1: Fix to allow keyboard search on load dialog. (type the first few letters of your save) Fixed check for new release. Changed the way ship details are loaded to alleviate load time for worlds with very large ships (100,000+ blocks). Fixed Image importer, was incorrectly listing 'Asteroid' as import option. Minor changes to menus (text and appearance) for clarity and OS consistency. Added in reading of world palette for color dialog editor. WIP on subsystem editor. Can now multiselec...Tiny Wifi Host: Tiny Wifi Host 3.0.0.0: Tiny Wifi Hotspot Creator (Portable) v3 size: 50KB-140KB New Features: Friendly name for connected devices instead of Mac-Address (Double click selected device to enter friendly name) Saves device names to devices.xml Better error reporting+solutions Warning sound when number of connected devices exceed a certain number. (useful when only certain number of devices must be connected at a time) Many Bug Fixes. NoAudio files does not include connect, disconnect and warning audio to dec...Media Companion: Media Companion MC3.597b: Thank you for being patient, againThere are a number of fixes in place with this release. and some new features added. Most are self explanatory, so check out the options in Preferences. Couple of new Features:* Movie - Allow save Title and Sort Title in Title Case format. * Movie - Allow save fanart.jpg if movie in folder. * TV - display episode source. Get episode source from episode filename. Fixed:* Movie - Added Fill Tags from plot keywords to Batch Rescraper. * Movie - Fixed TMDB s...SimCityPak: SimCityPak 0.3.0.0: Contains several bugfixes, newly identified properties and some UI improvements. Main new features UI overhaul for the main index list: Icons for each different index, including icons for different property files Tooltips for all relevant fields Removed clutter Identified hundreds of additional properties (thanks to MaxisGuillaume) - this should make modding gameplay easierNew ProjectsAlumno-Materia-Inscripcion: NADIA DEJATE DE JODEEERAndroid_Training_Leasing: Android Training LeasingBob The Simple Text Game: Bob The Simple Text Game is a Simple Text GameConference Booking System: Web application with the purpose of easily managing meetings in an office with multiple companiesCRM Web API Lead Capture Example: Sample Visual Studio 2013 project that provides an example of how you could use Web API and Microsoft Azure to capture HTML form data.FoosballEye: Foosball ranking application - allow to create simple ranking of foosball players base on played matches.Frequency Analyzer: Tool to perform frequency analysis on any text-based cryptogram. fromen_playground: We do stuff!!!!Galaktika ERP Helper: ??????????????? ???????, ??????????????? ??? ?????????? ?????????? ????????? ??????????, ???????????? ?????? ?? ??????? «????????? ERP»gitprojtest5132014: awdfHtml Markup Minifier (Orchard Module): Orchard module designed to reduce size of output HTML to bare minimum while maintaining same functionality. Faster loading, less bandwidth use.ID3 Hunter: The ID3 Hunter is a simple application that uses the Last.FM music database to automatically detect song metadata for MP3 files.Jquery Dirty Flag: Smart Way to Manage Dirty Flag Using JqueryJsxyUIS: ??????????????????????NetDirkFramework: NetDirkFramework?????.NET/ASP.NETMVC/WebAPI/ADO.NET/EF、jQuery?jEasyUI??????、??????MIS????????????。?????，?????????????????????????????????????????????。ocbizweb: ocbizwebPower Pole Survey: This is a showcase of my knowledge in MVVM Patterns.prestamosapi: prestamosapiRedLineTest: This is a test of the online collaboration tooling from MS. We are all using Visual Studio 2010.SharePoint Database Explorer: Connect to any SharePoint 2010 or 2013 content database to view and download documents, metadata and list items.Systematize: to arrange in accord with a definite plan or scheme : order systematically <the need to systematize their work>Visualizers: This project is used for how we want visualize our Data in debug mode For Visual studio 2010,zSILENCER: reverse MKULTRA??????-??????【??】??????????: ???????????????,????,???????、???????????,???????????,????,?????,???????。 ????-????【??】????????: ?????????????????????,????????????,?????、??、????,?????,??????！ ?????-?????【??】?????????: ???????????????????,???、???!???????,????????????????,????????????,???! ?????-?????【??】?????????: ????????????、?????、?????、?????、?????、????,???????????,?????,??????！ ????-????【??】????????: ????????【.????.????.????.????.】??【??】:、??、??、??、??、??、??、??、??、??、??、?????。 ??????-??????【??】??????????: ????????????????????????,????,????,????,???????,?????,?????.??????。 ??????-??????【??】??????????: ????????????????、?????,????????????????????,????,????,??????。 ????-????【??】????????: ????????????????,????,??.??.??.??.??.??.??.???，????，???????! ?????-?????【??】?????????: ???????????????????????????:???????,??????,????,????,????,?????！ ?????-?????【??】?????????: ?????????????,????????,?????,???,???????????,???????????,?????,??????！ ??????-??????【??】??????????: ??????????,??????????????????????,???????????????,?????????????！ ??????-??????【??】??????????: ??????????????????????,?????, ... ????????????,????,????,?????,???????。 ????-????【??】????????: ???????????????????，?????????/?,,???????????,??????????????! ?????-?????【??】?????????: ????????????????????,?????????、??、??、????,??????????,?????????????！ ?????-?????【??】?????????: ????????????????、????、????、??????????,???,?????,???????????????. ????-????【??】????????: ?????????????????,?????????????,????,?????????,?????????????,?????,?????! ??????-??????【??】??????????: ???????????,?????????????? ??。????????、????、????、?????????? ???????。 ??????-??????【??】??????????: ???????????????????????:????、????、??????????????,????????。????????! ????-????【??】????????: ????????????????、?????、?????、????、?????,??????????。????????????????! ?????-?????【??】?????????: ??????????????????????????,??????????,????,????,?????????、??????,??????。 ?????-?????【??】?????????: ????????????????????????????,??????????,????,????,?????????、??????,??????。

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• C#/.NET Little Wonders: Interlocked CompareExchange()

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Two posts ago, I discussed the Interlocked Add(), Increment(), and Decrement() methods (here) for adding and subtracting values in a thread-safe, lightweight manner.  Then, last post I talked about the Interlocked Read() and Exchange() methods (here) for safely and efficiently reading and setting 32 or 64 bit values (or references).  This week, we’ll round out the discussion by talking about the Interlocked CompareExchange() method and how it can be put to use to exchange a value if the current value is what you expected it to be. Dirty reads can lead to bad results Many of the uses of Interlocked that we’ve explored so far have centered around either reading, setting, or adding values.  But what happens if you want to do something more complex such as setting a value based on the previous value in some manner? Perhaps you were creating an application that reads a current balance, applies a deposit, and then saves the new modified balance, where of course you’d want that to happen atomically.  If you read the balance, then go to save the new balance and between that time the previous balance has already changed, you’ll have an issue!  Think about it, if we read the current balance as $400, and we are applying a new deposit of $50.75, but meanwhile someone else deposits $200 and sets the total to $600, but then we write a total of $450.75 we’ve lost $200! Now, certainly for int and long values we can use Interlocked.Add() to handles these cases, and it works well for that.  But what if we want to work with doubles, for example?  Let’s say we wanted to add the numbers from 0 to 99,999 in parallel.  We could do this by spawning several parallel tasks to continuously add to a total: 1: double total = 0; 2:  3: Parallel.For(0, 10000, next => 4: { 5: total += next; 6: }); Were this run on one thread using a standard for loop, we’d expect an answer of 4,999,950,000 (the sum of all numbers from 0 to 99,999).  But when we run this in parallel as written above, we’ll likely get something far off.  The result of one of my runs, for example, was 1,281,880,740.  That is way off!  If this were banking software we’d be in big trouble with our clients.  So what happened?  The += operator is not atomic, it will read in the current value, add the result, then store it back into the total.  At any point in all of this another thread could read a “dirty” current total and accidentally “skip” our add.   So, to clean this up, we could use a lock to guarantee concurrency: 1: double total = 0.0; 2: object locker = new object(); 3:  4: Parallel.For(0, count, next => 5: { 6: lock (locker) 7: { 8: total += next; 9: } 10: }); Which will give us the correct result of 4,999,950,000.  One thing to note is that locking can be heavy, especially if the operation being locked over is trivial, or the life of the lock is a high percentage of the work being performed concurrently.  In the case above, the lock consumes pretty much all of the time of each parallel task – and the task being locked on is relatively trivial. Now, let me put in a disclaimer here before we go further: For most uses, lock is more than sufficient for your needs, and is often the simplest solution!    So, if lock is sufficient for most needs, why would we ever consider another solution?  The problem with locking is that it can suspend execution of your thread while it waits for the signal that the lock is free.  Moreover, if the operation being locked over is trivial, the lock can add a very high level of overhead.  This is why things like Interlocked.Increment() perform so well, instead of locking just to perform an increment, we perform the increment with an atomic, lockless method. As with all things performance related, it’s important to profile before jumping to the conclusion that you should optimize everything in your path.  If your profiling shows that locking is causing a high level of waiting in your application, then it’s time to consider lighter alternatives such as Interlocked. CompareExchange() – Exchange existing value if equal some value So let’s look at how we could use CompareExchange() to solve our problem above.  The general syntax of CompareExchange() is: T CompareExchange<T>(ref T location, T newValue, T expectedValue) If the value in location == expectedValue, then newValue is exchanged.  Either way, the value in location (before exchange) is returned. Actually, CompareExchange() is not one method, but a family of overloaded methods that can take int, long, float, double, pointers, or references.  It cannot take other value types (that is, can’t CompareExchange() two DateTime instances directly).  Also keep in mind that the version that takes any reference type (the generic overload) only checks for reference equality, it does not call any overridden Equals(). So how does this help us?  Well, we can grab the current total, and exchange the new value if total hasn’t changed.  This would look like this: 1: // grab the snapshot 2: double current = total; 3:  4: // if the total hasn’t changed since I grabbed the snapshot, then 5: // set it to the new total 6: Interlocked.CompareExchange(ref total, current + next, current); So what the code above says is: if the amount in total (1st arg) is the same as the amount in current (3rd arg), then set total to current + next (2nd arg).  This check and exchange pair is atomic (and thus thread-safe). This works if total is the same as our snapshot in current, but the problem, is what happens if they aren’t the same?  Well, we know that in either case we will get the previous value of total (before the exchange), back as a result.  Thus, we can test this against our snapshot to see if it was the value we expected: 1: // if the value returned is != current, then our snapshot must be out of date 2: // which means we didn't (and shouldn't) apply current + next 3: if (Interlocked.CompareExchange(ref total, current + next, current) != current) 4: { 5: // ooops, total was not equal to our snapshot in current, what should we do??? 6: } So what do we do if we fail?  That’s up to you and the problem you are trying to solve.  It’s possible you would decide to abort the whole transaction, or perhaps do a lightweight spin and try again.  Let’s try that: 1: double current = total; 2:  3: // make first attempt... 4: if (Interlocked.CompareExchange(ref total, current + i, current) != current) 5: { 6: // if we fail, go into a spin wait, spin, and try again until succeed 7: var spinner = new SpinWait(); 8:  9: do 10: { 11: spinner.SpinOnce(); 12: current = total; 13: } 14: while (Interlocked.CompareExchange(ref total, current + i, current) != current); 15: } 16:  This is not trivial code, but it illustrates a possible use of CompareExchange().  What we are doing is first checking to see if we succeed on the first try, and if so great!  If not, we create a SpinWait and then repeat the process of SpinOnce(), grab a fresh snapshot, and repeat until CompareExchnage() succeeds.  You may wonder why not a simple do-while here, and the reason it’s more efficient to only create the SpinWait until we absolutely know we need one, for optimal efficiency. Though not as simple (or maintainable) as a simple lock, this will perform better in many situations.  Comparing an unlocked (and wrong) version, a version using lock, and the Interlocked of the code, we get the following average times for multiple iterations of adding the sum of 100,000 numbers: 1: Unlocked money average time: 2.1 ms 2: Locked money average time: 5.1 ms 3: Interlocked money average time: 3 ms So the Interlocked.CompareExchange(), while heavier to code, came in lighter than the lock, offering a good compromise of safety and performance when we need to reduce contention. CompareExchange() - it’s not just for adding stuff… So that was one simple use of CompareExchange() in the context of adding double values -- which meant we couldn’t have used the simpler Interlocked.Add() -- but it has other uses as well. If you think about it, this really works anytime you want to create something new based on a current value without using a full lock.  For example, you could use it to create a simple lazy instantiation implementation.  In this case, we want to set the lazy instance only if the previous value was null: 1: public static class Lazy<T> where T : class, new() 2: { 3: private static T _instance; 4:  5: public static T Instance 6: { 7: get 8: { 9: // if current is null, we need to create new instance 10: if (_instance == null) 11: { 12: // attempt create, it will only set if previous was null 13: Interlocked.CompareExchange(ref _instance, new T(), (T)null); 14: } 15:  16: return _instance; 17: } 18: } 19: } So, if _instance == null, this will create a new T() and attempt to exchange it with _instance.  If _instance is not null, then it does nothing and we discard the new T() we created. This is a way to create lazy instances of a type where we are more concerned about locking overhead than creating an accidental duplicate which is not used.  In fact, the BCL implementation of Lazy<T> offers a similar thread-safety choice for Publication thread safety, where it will not guarantee only one instance was created, but it will guarantee that all readers get the same instance.  Another possible use would be in concurrent collections.  Let’s say, for example, that you are creating your own brand new super stack that uses a linked list paradigm and is “lock free”.  We could use Interlocked.CompareExchange() to be able to do a lockless Push() which could be more efficient in multi-threaded applications where several threads are pushing and popping on the stack concurrently. Yes, there are already concurrent collections in the BCL (in .NET 4.0 as part of the TPL), but it’s a fun exercise!  So let’s assume we have a node like this: 1: public sealed class Node<T> 2: { 3: // the data for this node 4: public T Data { get; set; } 5:  6: // the link to the next instance 7: internal Node<T> Next { get; set; } 8: } Then, perhaps, our stack’s Push() operation might look something like: 1: public sealed class SuperStack<T> 2: { 3: private volatile T _head; 4:  5: public void Push(T value) 6: { 7: var newNode = new Node<int> { Data = value, Next = _head }; 8:  9: if (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next) 10: { 11: var spinner = new SpinWait(); 12:  13: do 14: { 15: spinner.SpinOnce(); 16: newNode.Next = _head; 17: } 18: while (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next); 19: } 20: } 21:  22: // ... 23: } Notice a similar paradigm here as with adding our doubles before.  What we are doing is creating the new Node with the data to push, and with a Next value being the original node referenced by _head.  This will create our stack behavior (LIFO – Last In, First Out).  Now, we have to set _head to now refer to the newNode, but we must first make sure it hasn’t changed! So we check to see if _head has the same value we saved in our snapshot as newNode.Next, and if so, we set _head to newNode.  This is all done atomically, and the result is _head’s original value, as long as the original value was what we assumed it was with newNode.Next, then we are good and we set it without a lock!  If not, we SpinWait and try again. Once again, this is much lighter than locking in highly parallelized code with lots of contention.  If I compare the method above with a similar class using lock, I get the following results for pushing 100,000 items: 1: Locked SuperStack average time: 6 ms 2: Interlocked SuperStack average time: 4.5 ms So, once again, we can get more efficient than a lock, though there is the cost of added code complexity.  Fortunately for you, most of the concurrent collection you’d ever need are already created for you in the System.Collections.Concurrent (here) namespace – for more information, see my Little Wonders – The Concurent Collections Part 1 (here), Part 2 (here), and Part 3 (here). Summary We’ve seen before how the Interlocked class can be used to safely and efficiently add, increment, decrement, read, and exchange values in a multi-threaded environment.  In addition to these, Interlocked CompareExchange() can be used to perform more complex logic without the need of a lock when lock contention is a concern. The added efficiency, though, comes at the cost of more complex code.  As such, the standard lock is often sufficient for most thread-safety needs.  But if profiling indicates you spend a lot of time waiting for locks, or if you just need a lock for something simple such as an increment, decrement, read, exchange, etc., then consider using the Interlocked class’s methods to reduce wait. Technorati Tags: C#,CSharp,.NET,Little Wonders,Interlocked,CompareExchange,threading,concurrency

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• ????ASMM

  - by Liu Maclean(???)

  ???Oracle??????????????SGA/PGA???,????10g????????????ASMM????,????????ASMM?????????Oracle??????????,?ASMM??????DBA????????????;????????ASMM???????????????DBA???:????????????DB,?????????????DBA?????????????????????????????????,ASMM??????????,???????????,??????????,??????????????????;?10g release 1?10.2??????ASMM?????????????,???????ASMM????????ASMM?????startup???????????ASMM??AMM??,????????DBA????SGA/PGA?????????”??”??”???”???,???????????DBA????chemist(???????1??2??????????????)? ?????????????????ASMM?????,?????????????…… Oracle?SGA???????9i???????????,????: Buffer Cache ????????????,??????????????? Default Pool                  ??????,???DB_CACHE_SIZE?? Keep Pool                     ??????,???DB_KEEP_CACHE_SIZE?? Non standard pool         ???????,???DB_nK_cache_size?? Recycle pool                 ???,???db_recycle_cache_size?? Shared Pool ???,???shared_pool_size?? Library cache   ?????? Row cache      ???,?????? Java Pool         java?,???Java_pool_size?? Large Pool       ??,???Large_pool_size?? Fixed SGA       ???SGA??,???Oracle???????,?????????granule? ?9i?????ASMM,???????????SGA,??????MSMM??9i???buffer cache??????????,?????????????????????????,???9i?????????????,?????????????????????????? ????SGA?????: ?????shared pool?default buffer pool????????,??????????? ?9i???????????(advisor),?????????? ??????????????? ?????????,?????? ?????,?????ORA-04031?????????? ASMM?????: ?????????? ???????????????? ???????sga_target?? ???????????,??????????? ??MSMM???????: ???? ???? ?????? ???? ??????????,??????????? ??????????????????,??????????ORA-04031??? ASMM???????????:1.??????sga_target???????2.???????,???:????(memory component),????(memory broker)???????(memory mechanism)3.????(memory advisor) ASMM????????????(Automatically set),??????:shared_pool_size?db_cache_size?java_pool_size?large_pool _size?streams_pool_size;?????????????????,???:db_keep_cache_size?db_recycle_cache_size?db_nk_cache_size?log_buffer????SGA?????,????????????????,??log_buffer?fixed sga??????????????? ??ASMM?????????sga_target??,???????ASMM??????????????????db_cache_size?java_pool_size???,?????????????????????,????????????????????(???)????????,Oracle?????????(granule,?SGA<1GB?granule???4M,?SGA>1GB?granule???16M)???????,??????????????buffer cache,??????????????????(granule)??????????????????????sga_target??,???????????????????(dism,???????)???ASMM?????????????statistics_level?????typical?ALL,?????BASIC??MMON????(Memory Monitor is a background process that gathers memory statistics (snapshots) stores this information in the AWR (automatic workload repository). MMON is also responsible for issuing alerts for metrics that exceed their thresholds)?????????????????????ASMM?????,???????????sga_target?????statistics_level?BASIC: SQL> show parameter sga NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ lock_sga boolean FALSE pre_page_sga boolean FALSE sga_max_size big integer 2000M sga_target big integer 2000M SQL> show parameter sga_target NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ sga_target big integer 2000M SQL> alter system set statistics_level=BASIC; alter system set statistics_level=BASIC * ERROR at line 1: ORA-02097: parameter cannot be modified because specified value is invalid ORA-00830: cannot set statistics_level to BASIC with auto-tune SGA enabled ?????server parameter file?spfile??,ASMM????shutdown??????????????(Oracle???????,????????)???spfile?,?????strings?????spfile????????????????????,?: G10R2.__db_cache_size=973078528 G10R2.__java_pool_size=16777216 G10R2.__large_pool_size=16777216 G10R2.__shared_pool_size=1006632960 G10R2.__streams_pool_size=67108864 ???spfile?????????????????,???????????”???”?????,??????????”??”?? ?ASMM?????????????? ?????(tunable):????????????????????????????buffer cache?????????,cache????????????????,?????????? IO????????????????????????????Library cache????? subheap????,?????????????????????????????????(open cursors)?????????client??????????????buffer cache???????,???????????pin??buffer???(???????) ?????(Un-tunable):???????????????????,?????????????????,?????????????????????????large pool?????? ??????(Fixed Size):???????????,??????????????????????????????????????? ????????????????(memory resize request)?????????,?????: ??????(Immediate Request):???????????ASMM????????????????????????(chunk)?,??????OUT-OF-MEMORY(ORA-04031)???,????????????????????(granule)????????????????????granule,????????????,?????????????????????????????,????granule??????????????? ??????(Deferred Request):???????????????????????????,??????????????granule???????????????MMON??????????delta. ??????(Manual Request):????????????alter system?????????????????????????????????????????????????granule,??????grow?????ORA-4033??,?????shrink?????ORA-4034??? ?ASMM????,????(Memory Broker)????????????????????????????(Deferred)??????????????????????(auto-tunable component)???????????????,???????????????MMON??????????????????????????????????,????????????????;MMON????Memory Broker?????????????????????????MMON????????????????????????????????????????(resize request system queue)?MMAN????(Memory Manager is a background process that manages the dynamic resizing of SGA memory areas as the workload increases or decreases)??????????????????? ?10gR1?Shared Pool?shrink??????????,?????????????Buffer Cache???????????granule,????Buffer Cache?granule????granule header?Metadata(???buffer header??RAC??Lock Elements)????,?????????????????????shared pool????????duration(?????)?chunk??????granule?,????????????granule??10gR2????Buffer Cache Granule????????granule header?buffer?Metadata(buffer header?LE)????,??shared pool???duration?chunk????????granule,??????buffer cache?shared pool??????????????10gr2?streams pool?????????(???????streams pool duration????) ??????????(Donor,???trace????)???,?????????granule???buffer cache,????granule????????????: ????granule???????granule header ?????chunk????granule?????????buffer header ???,???chunk??????????????????????metadata? ???2-4??,???granule???? ??????????????????,??buffer cache??granule???shared pool?,???????: MMAN??????????buffer cache???granule MMAN????granule??quiesce???(Moving 1 granule from inuse to quiesce list of DEFAULT buffer cache for an immediate req) DBWR???????quiesced???granule????buffer(dirty buffer) MMAN??shared pool????????(consume callback),granule?free?chunk???shared pool??(consume)?,????????????????????granule????shared granule??????,???????????granule???????????,??????pin??buffer??Metadata(???buffer header?LE)?????buffer cache??? ???granule???????shared pool,???granule?????shared??? ?????ASMM???????????,??????????: _enabled_shared_pool_duration:?????????10g????shared pool duration??,?????sga_target?0?????false;???10.2.0.5??cursor_space_for_time???true??????false,???10.2.0.5??cursor_space_for_time????? _memory_broker_shrink_heaps:???????0??Oracle?????shared pool?java pool,??????0,??shrink request??????????????????? _memory_management_tracing: ???????MMON?MMAN??????????(advisor)?????(Memory Broker)?????trace???;??ORA-04031????????36,???8?????????????trace,???23????Memory Broker decision???,???32???cache resize???;??????????: Level Contents 0×01 Enables statistics tracing 0×02 Enables policy tracing 0×04 Enables transfer of granules tracing 0×08 Enables startup tracing 0×10 Enables tuning tracing 0×20 Enables cache tracing ?????????_memory_management_tracing?????DUMP_TRANSFER_OPS????????????????,?????????????????trace?????????mman_trace?transfer_ops_dump? SQL> alter system set "_memory_management_tracing"=63; System altered Operation make shared pool grow and buffer cache shrink!!!.............. ???????granule?????,????default buffer pool?resize??: AUTO SGA: Request 0xdc9c2628 after pre-processing, ret=0 /* ???0xdc9c2628??????addr */ AUTO SGA: IMMEDIATE, FG request 0xdc9c2628 /* ???????????Immediate???? */ AUTO SGA: Receiver of memory is shared pool, size=16, state=3, flg=0 /* ?????????shared pool,???,????16?granule,??grow?? */ AUTO SGA: Donor of memory is DEFAULT buffer cache, size=106, state=4, flg=0 /* ???????Default buffer cache,????,????106?granule,??shrink?? */ AUTO SGA: Memory requested=3896, remaining=3896 /* ??immeidate request???????3896 bytes */ AUTO SGA: Memory received=0, minreq=3896, gransz=16777216 /* ????free?granule,??received?0,gransz?granule??? */ AUTO SGA: Request 0xdc9c2628 status is INACTIVE /* ??????????,??????inactive?? */ AUTO SGA: Init bef rsz for request 0xdc9c2628 /* ????????before-process???? */ AUTO SGA: Set rq dc9c2628 status to PENDING /* ?request??pending?? */ AUTO SGA: 0xca000000 rem=3896, rcvd=16777216, 105, 16777216, 17 /* ???????0xca000000?16M??granule */ AUTO SGA: Returning 4 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 4, 1, a AUTO SGA: Resize done for pool DEFAULT, 8192 /* ???default pool?resize */ AUTO SGA: Init aft rsz for request 0xdc9c2628 AUTO SGA: Request 0xdc9c2628 after processing AUTO SGA: IMMEDIATE, FG request 0x7fff917964a0 AUTO SGA: Receiver of memory is shared pool, size=17, state=0, flg=0 AUTO SGA: Donor of memory is DEFAULT buffer cache, size=105, state=0, flg=0 AUTO SGA: Memory requested=3896, remaining=0 AUTO SGA: Memory received=16777216, minreq=3896, gransz=16777216 AUTO SGA: Request 0x7fff917964a0 status is COMPLETE /* shared pool????16M?granule */ AUTO SGA: activated granule 0xca000000 of shared pool ?????partial granule????????????trace: AUTO SGA: Request 0xdc9c2628 after pre-processing, ret=0 AUTO SGA: IMMEDIATE, FG request 0xdc9c2628 AUTO SGA: Receiver of memory is shared pool, size=82, state=3, flg=1 AUTO SGA: Donor of memory is DEFAULT buffer cache, size=36, state=4, flg=1 /* ????????shared pool,?????default buffer cache */ AUTO SGA: Memory requested=4120, remaining=4120 AUTO SGA: Memory received=0, minreq=4120, gransz=16777216 AUTO SGA: Request 0xdc9c2628 status is INACTIVE AUTO SGA: Init bef rsz for request 0xdc9c2628 AUTO SGA: Set rq dc9c2628 status to PENDING AUTO SGA: Moving granule 0x93000000 of DEFAULT buffer cache to activate list AUTO SGA: Moving 1 granule 0x8c000000 from inuse to quiesce list of DEFAULT buffer cache for an immediate req /* ???buffer cache??????0x8c000000?granule??????inuse list, ???????quiesce list? */ AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: activated granule 0x93000000 of DEFAULT buffer cache AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 / * ??dbwr??0x8c000000 granule????dirty buffer */ AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 AUTO SGA: Returning 0 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 0, 1, 20a AUTO SGA: NOT_FREE for imm req for gran 0x8c000000 ......................................... AUTO SGA: Rcv shared pool consuming 8192 from 0x8c000000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 90112 from 0x8c002000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 24576 from 0x8c01a000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 65536 from 0x8c022000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 131072 from 0x8c034000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 286720 from 0x8c056000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 98304 from 0x8c09e000 in granule 0x8c000000; owner is DEFAULT buffer cache AUTO SGA: Rcv shared pool consuming 106496 from 0x8c0b8000 in granule 0x8c000000; owner is DEFAULT buffer cache ..................... /* ??shared pool????0x8c000000 granule??chunk, ??granule?owner????default buffer cache */ AUTO SGA: Imm xfer 0x8c000000 from quiesce list of DEFAULT buffer cache to partial inuse list of shared pool /* ???0x8c000000 granule?default buffer cache????????shared pool????inuse list */ AUTO SGA: Returning 4 from kmgs_process for request dc9c2628 AUTO SGA: Process req dc9c2628 ret 4, 1, 20a AUTO SGA: Init aft rsz for request 0xdc9c2628 AUTO SGA: Request 0xdc9c2628 after processing AUTO SGA: IMMEDIATE, FG request 0x7fffe9bcd0e0 AUTO SGA: Receiver of memory is shared pool, size=83, state=0, flg=1 AUTO SGA: Donor of memory is DEFAULT buffer cache, size=35, state=0, flg=1 AUTO SGA: Memory requested=4120, remaining=0 AUTO SGA: Memory received=14934016, minreq=4120, gransz=16777216 AUTO SGA: Request 0x7fffe9bcd0e0 status is COMPLETE /* ????partial transfer?? */ ?????partial transfer??????DUMP_TRANSFER_OPS????0x8c000000 partial granule???????,?: SQL> oradebug setmypid; Statement processed. SQL> oradebug dump DUMP_TRANSFER_OPS 1; Statement processed. SQL> oradebug tracefile_name; /s01/admin/G10R2/udump/g10r2_ora_21482.trc =======================trace content============================== GRANULE SIZE is 16777216 COMPONENT NAME : shared pool Number of granules in partially inuse list (listid 4) is 23 Granule addr is 0x8c000000 Granule owner is DEFAULT buffer cache /* ?0x8c000000 granule?shared pool?partially inuse list, ?????owner??default buffer cache */ Granule 0x8c000000 dump from owner perspective gptr = 0x8c000000, num buf hdrs = 1989, num buffers = 156, ghdr = 0x8cffe000 / * ?????granule?granule header????0x8cffe000, ????156?buffer block,1989?buffer header */ /* ??granule??????,??????buffer cache??shared pool chunk */ BH:0x8cf76018 BA:(nil) st:11 flg:20000 BH:0x8cf76128 BA:(nil) st:11 flg:20000 BH:0x8cf76238 BA:(nil) st:11 flg:20000 BH:0x8cf76348 BA:(nil) st:11 flg:20000 BH:0x8cf76458 BA:(nil) st:11 flg:20000 BH:0x8cf76568 BA:(nil) st:11 flg:20000 BH:0x8cf76678 BA:(nil) st:11 flg:20000 BH:0x8cf76788 BA:(nil) st:11 flg:20000 BH:0x8cf76898 BA:(nil) st:11 flg:20000 BH:0x8cf769a8 BA:(nil) st:11 flg:20000 BH:0x8cf76ab8 BA:(nil) st:11 flg:20000 BH:0x8cf76bc8 BA:(nil) st:11 flg:20000 BH:0x8cf76cd8 BA:0x8c018000 st:1 flg:622202 ............... Address 0x8cf30000 to 0x8cf74000 not in cache Address 0x8cf74000 to 0x8d000000 in cache Granule 0x8c000000 dump from receivers perspective Dumping layout Address 0x8c000000 to 0x8c018000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c018000 to 0x8c01a000 not in this pool Address 0x8c01a000 to 0x8c020000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c020000 to 0x8c022000 not in this pool Address 0x8c022000 to 0x8c032000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c032000 to 0x8c034000 not in this pool Address 0x8c034000 to 0x8c054000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c054000 to 0x8c056000 not in this pool Address 0x8c056000 to 0x8c09c000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c09c000 to 0x8c09e000 not in this pool Address 0x8c09e000 to 0x8c0b6000 in sga heap(1,3) (idx=1, dur=4) Address 0x8c0b6000 to 0x8c0b8000 not in this pool Address 0x8c0b8000 to 0x8c0d2000 in sga heap(1,3) (idx=1, dur=4) ???????granule?????shared granule??????,?????????buffer block,????1?shared subpool??????durtaion?4?chunk,duration=4?execution duration;??duration?chunk???????????,??extent???quiesce list??????????????free?execution duration?????????????,??????duration???extent(??????extent????granule)??????? ?????????????ASMM?????????,????: V$SGAINFODisplays summary information about the system global area (SGA). V$SGADisplays size information about the SGA, including the sizes of different SGA components, the granule size, and free memory. V$SGASTATDisplays detailed information about the SGA. V$SGA_DYNAMIC_COMPONENTSDisplays information about the dynamic SGA components. This view summarizes information based on all completed SGA resize operations since instance startup. V$SGA_DYNAMIC_FREE_MEMORYDisplays information about the amount of SGA memory available for future dynamic SGA resize operations. V$SGA_RESIZE_OPSDisplays information about the last 400 completed SGA resize operations. V$SGA_CURRENT_RESIZE_OPSDisplays information about SGA resize operations that are currently in progress. A resize operation is an enlargement or reduction of a dynamic SGA component. V$SGA_TARGET_ADVICEDisplays information that helps you tune SGA_TARGET. ?????????shared pool duration???,?????????

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• Return HTTP 404 when MVC2 view does not exist

  - by Dmitriy Nagirnyak

  Hi, I just need to have the a small CMS-like controller. The easiest way would be something like this: public class HomeController : Controller { public ActionResult View(string name) { if (!ViewExists(name)) return new HttpNotFoundResult(); return View(name); } private bool ViewExists(string name) { // How to check if the view exists without checking the file itself? } } The question is how to return HTTP 404 if the there is no view available? Probably I can check the files in appropriate locations and cache the result, but that feels really dirty. Thanks, Dmitriy.

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• Does Powershell have an "eval" equivalent? Is there a better way to see a list of properties and val

  - by glenatron

  I'm doing a bit of Powershell scripting ( for the first time ) to look at some stuff in a Sharepoint site and what I would like to be able to do is to go through a list of properties of an object and just output their values in a "property-name = value" kind of format. Now I can find the list of elements using this: $myObject | get-member -membertype property Which will return a list of all the properties in a very clear and readable fashion. But what I need is to find a value for those properties. In some scripting languages I could have a kind of eval( "$myObject.$propertyName" ) call - where I have extracted $propertyName from the get-member output - and have it evaluate the string as code, which for the kind of quick-and-dirty solution I need would be fine. Does this exist in Powershell or is there a more convenient way to do it? Should I be using reflection instead?

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• Setting the value (selected option) of a dijit.form.Select widget

  - by Wahnfrieden

  I have a dijit.form.Select widget. It's tied to a data store, if that matters. It's filled with several options already. All I want to do is programmatically set its value. I can get its value using myWidget.attr('value') but if I try to do myWidget.attr('value', 5) for example (where 5 is one of the valid values), all it does is reset the widget to select the very first option, no matter what value I give it. This seems to be a bug, and there aren't any tests or documentation which show how to accomplish what I want to. But is there some way, even if it's a dirty hack? I'm using Dojo 1.4.0. Note that dijit.form.Select is the new name for dojox.form.DropDownSelect. edit: I even tried resetting the widget with all new options, but it ignores the option which has selected = true and just selects the first option. There must still be a way though.

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• Identify in a unit test if Jetbrains IntelliJ IDEA 8 or 9 is running

  - by Ran Biron

  I need to know, in a context of a unit test, if Jetbrains IntelliJ idea is the test initiator and if it is, which version is running (or at least if it's "9" or earlier). I don't mind doing dirty tricks (reflection, filesystem, environment...) but I do need this to work "out-of-the-box" (without each developer having to setup something special). I've tried some reflection but couldn't find a unique identifier I could latch onto. Any idea? Oh - the language is Java.

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• How to create a new LaTeX command that behaves something like \verb?

  - by NawaMan

  I have been using LaTeX from sometime now, but have never actually gotten my hands dirty declaring a new command, as I try to avoid that. However, I need to add monospace text often in my document and I use \verb for it which is fine, except that the verb font size is bigger than the normal text font. So I need to change the font size and undo done like \small{}\verb#My monospace code#\normalsize{}. This is not very convenient and mistake-prone. Is there a better way to do this? Can I define a new command for this? How?

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• QTableWidget signal cellChanged(): distinguish between user input and change by routines

  - by crabman

  i am using PyQt but my question is a general Qt one: I have a QTableWidget that is set up by the function updateTable. It writes the data from DATASET to the table when it is called. Unfortunately this causes my QTableWidget to emit the signal cellChanged() for every cell. The signal cellChanged() is connected to a function on_tableWidget_cellChanged that reads the contents of the changed cell and writes it back to DATASET. This is necessary to allow the user to change the data manually. So everytime the table is updated, its contents are written back to DATASET. Is there a way to distinguish if the cell was changed by the user or by updateTable? i thought of disconnecting on_tableWidget_cellChanged by updateTable temporarily but that seems to be a little dirty.

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• tortoisehg and subrepos

  - by adrianm

  I can't get Tortoisehg (1.0) to work with subrepos I have a directory structure like this: root .hg .hgsub .hgsubstate Customer1 Project1 .hg foo.txt Project2 .hg Customer2 Project3 .hg the .hgsub file under root looks like Customer1\Project1=Customer1\Project1 Customer1\Project2=Customer1\Project2 Customer2\Project3=Customer2\Project3 If modify the file Customer1\Project1\foo.txt and commit from the root it works >hg ci -m "command line commit" committing subrepository customer1\project1 in Tortoisehg customer1\project1 is displayed with status S (subrepo) but when commiting I get a message abort: customer1/project1: no match under directory! Is this scenario not supported or am I doing something wrong? The doc says: "TortoiseHg 1.0 introduced rudimentary support for subrepositories, and only in the commit / status tool. When Mercurial considers a subrepo as dirty, it will appear in the commit tool as a special entry in the file list with a status of S. If a subrepo is included in the file list of a commit, the subrepo is committed along with the other changes, updating the .hgsubstate file in the main repository root."

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• Android ConnectivityManager information

  - by Mike

  I am trying to get a better grip on Android's ConnectivityManager and how it really works under the hood. Using the API is simple enough but I am looking for something lower level such as when it starts and the dirty details of what its doing in the background. I can't seem to find a good resource about it. Everything is just about using the API. Does anyone understand this or have any resources that they could point me to, website, book, white paper, or otherwise? I would really appreciate it. Thanks

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• Android XMLRPC Fault Code

  - by sameersegal

  Hey, We have been using XMLRPC for android and it was working well until we got our hands dirty with Base64 encoding for byte[] (images) -- (we did base64_string.replace("/","$$") for transmission). We have tried undoing the changes and its looking an XMLRPC error. We are getting the following error in the DDMS: 06-10 23:27:02.970: DEBUG/Test(343): org.xmlrpc.android.XMLRPCFault: XMLRPC Fault: [code 0] 06-10 23:27:02.970: DEBUG/Test(343): at org.xmlrpc.android.XMLRPCClient.callEx(XMLRPCClient.java:308) 06-10 23:27:02.970: DEBUG/Test(343): at org.xmlrpc.android.XMLRPCMethod.run(XMLRPCMethod.java:33) Just before this I checked the body (xml message -- which is perfect) and the response received: 06-10 23:27:02.940: INFO/System.out(343): Response received: org.apache.http.message.BasicHttpResponse@437762f8 Since it the message is not even reaching our cloud, the issue is with XMLRPC for android. Any help will be most appreciated. Thanks Best Sameer

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• Boost asio async vs blocking reads, udp speed/quality

  - by Dolphin

  I have a quick and dirty proof of concept app that I wrote in C# that reads high data rate multicast UDP packets from the network. For various reasons the full implementation will be written in C++ and I am considering using boost asio. The C# version used a thread to receive the data using blocking reads. I had some problems with dropped packets if the computer was heavily loaded (generally with processing those packets in another thread). What I would like to know is if the async read operations in boost (which use overlapped io in windows) will help ensure that I receive the packets and/or reduce the cpu time needed to receive the packets. The single thread doing blocking reads is pretty straightforward, using the async reads seems like a step up in complexity, but I think it would be worth it if it provided higher performance or dropped fewer packets on a heavily loaded system. Currently the data rate should be no higher than 60Mb/s.

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• Nice name for `decorator' class?

  - by Lajos Nagy

  I would like to separate the API I'm working on into two sections: 'bare-bones' and 'cushy'. The idea is that all method calls in the 'cushy' section could be expressed in terms of the ones in the 'bare-bones' section, that is, they would only serve as convenience methods for the quick-and-dirty. The reason I would like to do this is that very often when people are beginning to use an API for the first time, they are not interested in details and performance: they just want to get it working. Anybody tried anything similar before? I'm particularly interested in naming conventions and organizing the code.

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