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  • Lock file/content while being edited in browser. [migrated]

    - by codescope
    In one of my projects users are allowed to edit the same file. It is group work and max number of users in group is 4. It is rare that they will be editing at the same time but there is possibility of it. I am using ckeditor which displays the content. how I can lock the content while it is being edited? For the above case what will happen if one users open the content for editing and then never saves and leave window open. Is it possible to save the content, release the lock for editing by another users? If first user comes back to desk they should see the message that "content has been changed, please refresh". I am using php, mysql. Thanks

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  • Mysql with innodb and serializable transaction does not (always) lock rows

    - by Tobias G.
    Hello, I have a transaction with a SELECT and possible INSERT. For concurrency reasons, I added FOR UPDATE to the SELECT. To prevent phantom rows, I'm using the SERIALIZABLE transaction isolation level. This all works fine when there are any rows in the table, but not if the table is empty. When the table is empty, the SELECT FOR UPDATE does not do any (exclusive) locking and a concurrent thread/process can issue the same SELECT FOR UPDATE without being locked. CREATE TABLE t ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, display_order INT ) ENGINE = InnoDB; SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION; SELECT COALESCE(MAX(display_order), 0) + 1 from t FOR UPDATE; .. This concept works as expected with SQL Server, but not with MySQL. Any ideas on what I'm doing wrong? EDIT Adding an index on display_order does not change the behavior.

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  • UIAlertView popups lock up keyboard actions

    - by TurbZ
    I have a strange behavior where if a UIAlert fires (like the one below) all subsequent keyboard or press behaviors are disabled / non responsive. Scrolling the screen still works but no action is fired from any button or keyboard presses. [[[[UIAlertView alloc] initWithTitle:@"Invalid Address" message:@"The email address you entered isn't valid. Please check and try again." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease] show]; Anyone experienced this behavior before and can shed some light? Or maybe guide me in the right direction to debug it further to get to the root cause? Thank you heaps!

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  • The case of the phantom ADF developer (and other yarns)

    - by Chris Muir
    A few years of ADF experience means I see common mistakes made by different developers, some I regularly make myself.  This post is designed to assist beginners to Oracle JDeveloper Application Development Framework (ADF) avoid a common ADF pitfall, the case of the phantom ADF developer [add Scooby-Doo music here]. ADF Business Components - triggers, default table values and instead of views. Oracle's JDeveloper tutorials help with the A-B-Cs of ADF development, typically built on the nice 'n safe demo schema provided by with the Oracle database such as the HR demo schema. However it's not too long until ADF beginners, having built up some confidence from learning with the tutorials and vanilla demo schemas, start building ADF Business Components based upon their own existing database schema objects.  This is where unexpected problems can sneak in. The crime Developers may encounter a surprising error at runtime when editing a record they just created or updated and committed to the database, based on their own existing tables, namely the error: JBO-25014: Another user has changed the row with primary key oracle.jbo.Key[x] ...where X is the primary key value of the row at hand.  In a production environment with multiple users this error may be legit, one of the other users has updated the row since you queried it.  Yet in a development environment this error is just plain confusing.  If developers are isolated in their own database, creating and editing records they know other users can't possibly be working with, or all the other developers have gone home for the day, how is this error possible? There are no other users?  It must be the phantom ADF developer! [insert dramatic music here] The following picture is what you'll see in the Business Component Browser, and you'll receive a similar error message via an ADF Faces page: A false conclusion What can possibly cause this issue if it isn't our phantom ADF developer?  Doesn't ADF BC implement record locking, locking database records when the row is modified in the ADF middle-tier by a user?  How can our phantom ADF developer even take out a lock if this is the case?  Maybe ADF has a bug, maybe ADF isn't implementing record locking at all?  Shouldn't we see the error "JBO-26030: Failed to lock the record, another user holds the lock" as we attempt to modify the record, why do we see JBO-25014? : Let's verify that ADF is in fact issuing the correct SQL LOCK-FOR-UPDATE statement to the database. First we need to verify ADF's locking strategy.  It is determined by the Application Module's jbo.locking.mode property.  The default (as of JDev 11.1.1.4.0 if memory serves me correct) and recommended value is optimistic, and the other valid value is pessimistic. Next we need a mechanism to check that ADF is issuing the LOCK statements to the database.  We could ask DBAs to monitor locks with OEM, but optimally we'd rather not involve overworked DBAs in this process, so instead we can use the ADF runtime setting –Djbo.debugoutput=console.  At runtime this options turns on instrumentation within the ADF BC layer, which among a lot of extra detail displayed in the log window, will show the actual SQL statement issued to the database, including the LOCK statement we're looking to confirm. Setting our locking mode to pessimistic, opening the Business Components Browser of a JSF page allowing us to edit a record, say the CHARGEABLE field within a BOOKINGS record where BOOKING_NO = 1206, upon editing the record see among others the following log entries: [421] Built select: 'SELECT BOOKING_NO, EVENT_NO, RESOURCE_CODE, CHARGEABLE, MADE_BY, QUANTITY, COST, STATUS, COMMENTS FROM BOOKINGS Bookings'[422] Executing LOCK...SELECT BOOKING_NO, EVENT_NO, RESOURCE_CODE, CHARGEABLE, MADE_BY, QUANTITY, COST, STATUS, COMMENTS FROM BOOKINGS Bookings WHERE BOOKING_NO=:1 FOR UPDATE NOWAIT[423] Where binding param 1: 1206  As can be seen on line 422, in fact a LOCK-FOR-UPDATE is indeed issued to the database.  Later when we commit the record we see: [441] OracleSQLBuilder: SAVEPOINT 'BO_SP'[442] OracleSQLBuilder Executing, Lock 1 DML on: BOOKINGS (Update)[443] UPDATE buf Bookings>#u SQLStmtBufLen: 210, actual=62[444] UPDATE BOOKINGS Bookings SET CHARGEABLE=:1 WHERE BOOKING_NO=:2[445] Update binding param 1: N[446] Where binding param 2: 1206[447] BookingsView1 notify COMMIT ... [448] _LOCAL_VIEW_USAGE_model_Bookings_ResourceTypesView1 notify COMMIT ... [449] EntityCache close prepared statement ....and as a result the changes are saved to the database, and the lock is released. Let's see what happens when we use the optimistic locking mode, this time to change the same BOOKINGS record CHARGEABLE column again.  As soon as we edit the record we see little activity in the logs, nothing to indicate any SQL statement, let alone a LOCK has been taken out on the row. However when we save our records by issuing a commit, the following is recorded in the logs: [509] OracleSQLBuilder: SAVEPOINT 'BO_SP'[510] OracleSQLBuilder Executing doEntitySelect on: BOOKINGS (true)[511] Built select: 'SELECT BOOKING_NO, EVENT_NO, RESOURCE_CODE, CHARGEABLE, MADE_BY, QUANTITY, COST, STATUS, COMMENTS FROM BOOKINGS Bookings'[512] Executing LOCK...SELECT BOOKING_NO, EVENT_NO, RESOURCE_CODE, CHARGEABLE, MADE_BY, QUANTITY, COST, STATUS, COMMENTS FROM BOOKINGS Bookings WHERE BOOKING_NO=:1 FOR UPDATE NOWAIT[513] Where binding param 1: 1205[514] OracleSQLBuilder Executing, Lock 2 DML on: BOOKINGS (Update)[515] UPDATE buf Bookings>#u SQLStmtBufLen: 210, actual=62[516] UPDATE BOOKINGS Bookings SET CHARGEABLE=:1 WHERE BOOKING_NO=:2[517] Update binding param 1: Y[518] Where binding param 2: 1205[519] BookingsView1 notify COMMIT ... [520] _LOCAL_VIEW_USAGE_model_Bookings_ResourceTypesView1 notify COMMIT ... [521] EntityCache close prepared statement Again even though we're seeing the midtier delay the LOCK statement until commit time, it is in fact occurring on line 412, and released as part of the commit issued on line 419.  Therefore with either optimistic or pessimistic locking a lock is indeed issued. Our conclusion at this point must be, unless there's the unlikely cause the LOCK statement is never really hitting the database, or the even less likely cause the database has a bug, then ADF does in fact take out a lock on the record before allowing the current user to update it.  So there's no way our phantom ADF developer could even modify the record if he tried without at least someone receiving a lock error. Hmm, we can only conclude the locking mode is a red herring and not the true cause of our problem.  Who is the phantom? At this point we'll need to conclude that the error message "JBO-25014: Another user has changed" is somehow legit, even though we don't understand yet what's causing it. This leads onto two further questions, how does ADF know another user has changed the row, and what's been changed anyway? To answer the first question, how does ADF know another user has changed the row, the Fusion Guide's section 4.10.11 How to Protect Against Losing Simultaneous Updated Data , that details the Entity Object Change-Indicator property, gives us the answer: At runtime the framework provides automatic "lost update" detection for entity objects to ensure that a user cannot unknowingly modify data that another user has updated and committed in the meantime. Typically, this check is performed by comparing the original values of each persistent entity attribute against the corresponding current column values in the database at the time the underlying row is locked. Before updating a row, the entity object verifies that the row to be updated is still consistent with the current state of the database.  The guide further suggests to make this solution more efficient: You can make the lost update detection more efficient by identifying any attributes of your entity whose values you know will be updated whenever the entity is modified. Typical candidates include a version number column or an updated date column in the row.....To detect whether the row has been modified since the user queried it in the most efficient way, select the Change Indicator option to compare only the change-indicator attribute values. We now know that ADF BC doesn't use the locking mechanism at all to protect the current user against updates, but rather it keeps a copy of the original record fetched, separate to the user changed version of the record, and it compares the original record against the one in the database when the lock is taken out.  If values don't match, be it the default compare-all-columns behaviour, or the more efficient Change Indicator mechanism, ADF BC will throw the JBO-25014 error. This leaves one last question.  Now we know the mechanism under which ADF identifies a changed row, what we don't know is what's changed and who changed it? The real culprit What's changed?  We know the record in the mid-tier has been changed by the user, however ADF doesn't use the changed record in the mid-tier to compare to the database record, but rather a copy of the original record before it was changed.  This leaves us to conclude the database record has changed, but how and by who? There are three potential causes: Database triggers The database trigger among other uses, can be configured to fire PLSQL code on a database table insert, update or delete.  In particular in an insert or update the trigger can override the value assigned to a particular column.  The trigger execution is actioned by the database on behalf of the user initiating the insert or update action. Why this causes the issue specific to our ADF use, is when we insert or update a record in the database via ADF, ADF keeps a copy of the record written to the database.  However the cached record is instantly out of date as the database triggers have modified the record that was actually written to the database.  Thus when we update the record we just inserted or updated for a second time to the database, ADF compares its original copy of the record to that in the database, and it detects the record has been changed – giving us JBO-25014. This is probably the most common cause of this problem. Default values A second reason this issue can occur is another database feature, default column values.  When creating a database table the schema designer can define default values for specific columns.  For example a CREATED_BY column could be set to SYSDATE, or a flag column to Y or N.  Default values are only used by the database when a user inserts a new record and the specific column is assigned NULL.  The database in this case will overwrite the column with the default value. As per the database trigger section, it then becomes apparent why ADF chokes on this feature, though it can only specifically occur in an insert-commit-update-commit scenario, not the update-commit-update-commit scenario. Instead of trigger views I must admit I haven't double checked this scenario but it seems plausible, that of the Oracle database's instead of trigger view (sometimes referred to as instead of views).  A view in the database is based on a query, and dependent on the queries complexity, may support insert, update and delete functionality to a limited degree.  In order to support fully insertable, updateable and deletable views, Oracle introduced the instead of view, that gives the view designer the ability to not only define the view query, but a set of programmatic PLSQL triggers where the developer can define their own logic for inserts, updates and deletes. While this provides the database programmer a very powerful feature, it can cause issues for our ADF application.  On inserting or updating a record in the instead of view, the record and it's data that goes in is not necessarily the data that comes out when ADF compares the records, as the view developer has the option to practically do anything with the incoming data, including throwing it away or pushing it to tables which aren't used by the view underlying query for fetching the data. Readers are at this point reminded that this article is specifically about how the JBO-25014 error occurs in the context of 1 developer on an isolated database.  The article is not considering how the error occurs in a production environment where there are multiple users who can cause this error in a legitimate fashion.  Assuming none of the above features are the cause of the problem, and optimistic locking is turned on (this error is not possible if pessimistic locking is the default mode *and* none of the previous causes are possible), JBO-25014 is quite feasible in a production ADF application if 2 users modify the same record. At this point under project timelines pressure, the obvious fix for developers is to drop both database triggers and default values from the underlying tables.  However we must be careful that these legacy constructs aren't used and assumed to be in place by other legacy systems.  Dropping the database triggers or default value that the existing Oracle Forms  applications assumes and requires to be in place could cause unexpected behaviour and bugs in the Forms application.  Proficient software engineers would recognize such a change may require a partial or full regression test of the existing legacy system, a potentially costly and timely exercise, not ideal. Solving the mystery once and for all Luckily ADF has built in functionality to deal with this issue, though it's not a surprise, as Oracle as the author of ADF also built the database, and are fully aware of the Oracle database's feature set.  At the Entity Object attribute level, the Refresh After Insert and Refresh After Update properties.  Simply selecting these instructs ADF BC after inserting or updating a record to the database, to expect the database to modify the said attributes, and read a copy of the changed attributes back into its cached mid-tier record.  Thus next time the developer modifies the current record, the comparison between the mid-tier record and the database record match, and JBO-25014: Another user has changed" is no longer an issue. [Post edit - as per the comment from Oracle's Steven Davelaar below, as he correctly points out the above solution will not work for instead-of-triggers views as it relies on SQL RETURNING clause which is incompatible with this type of view] Alternatively you can set the Change Indicator on one of the attributes.  This will work as long as the relating column for the attribute in the database itself isn't inadvertently updated.  In turn you're possibly just masking the issue rather than solving it, because if another developer turns the Change Indicator back on the original issue will return.

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  • Mysql SELECT FOR UPDATE - strange issue

    - by Michal Fronczyk
    Hi, I have a strange issue (at least for me :)) with the MySQL's locking facility. I have a table: Create Table: CREATE TABLE test ( id int(11) NOT NULL AUTO_INCREMENT, PRIMARY KEY (id) ) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=latin1 With this data: +----+ | id | +----+ | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 10 | | 11 | | 12 | +----+ Now I have 2 clients with these commands executed at the beginning: set autocommit=0; set session transaction isolation level serializable; begin; Now the most interesting part. The first client executes this query: (makes an intent to insert a row with id equal to 9) SELECT * from test where id = 9 FOR UPDATE; Empty set (0.00 sec) Then the second client does the same: SELECT * from test where id = 9 FOR UPDATE; Empty set (0.00 sec) My question is: Why the second client does not block ? An exclusive gap lock should have been set by the first query because FOR UPDATE have been used and the second client should block. If I am wrong, could somebody tell me how to do it correctly ? The MySql version I use is: 5.1.37-1ubuntu5.1 Thanks, Michal

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  • In Perl, how can I wait for threads to end in parallel?

    - by Pmarcoen
    I have a Perl script that launches 2 threads,one for each processor. I need it to wait for a thread to end, if one thread ends a new one is spawned. It seems that the join method blocks the rest of the program, therefore the second thread can't end until everything the first thread does is done which sort of defeats its purpose. I tried the is_joinable method but that doesn't seem to do it either. Here is some of my code : use threads; use threads::shared; @file_list = @ARGV; #Our file list $nofiles = $#file_list + 1; #Real number of files $currfile = 1; #Current number of file to process my %MSG : shared; #shared hash $thr0 = threads->new(\&process, shift(@file_list)); $currfile++; $thr1 = threads->new(\&process, shift(@file_list)); $currfile++; while(1){ if ($thr0->is_joinable()) { $thr0->join; #check if there are files left to process if($currfile <= $nofiles){ $thr0 = threads->new(\&process, shift(@file_list)); $currfile++; } } if ($thr1->is_joinable()) { $thr1->join; #check if there are files left to process if($currfile <= $nofiles){ $thr1 = threads->new(\&process, shift(@file_list)); $currfile++; } } } sub process{ print "Opening $currfile of $nofiles\n"; #do some stuff if(some condition){ lock(%MSG); #write stuff to hash } print "Closing $currfile of $nofiles\n"; } The output of this is : Opening 1 of 4 Opening 2 of 4 Closing 1 of 4 Opening 3 of 4 Closing 3 of 4 Opening 4 of 4 Closing 2 of 4 Closing 4 of 4

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  • Inside the Concurrent Collections: ConcurrentBag

    - by Simon Cooper
    Unlike the other concurrent collections, ConcurrentBag does not really have a non-concurrent analogy. As stated in the MSDN documentation, ConcurrentBag is optimised for the situation where the same thread is both producing and consuming items from the collection. We'll see how this is the case as we take a closer look. Again, I recommend you have ConcurrentBag open in a decompiler for reference. Thread Statics ConcurrentBag makes heavy use of thread statics - static variables marked with ThreadStaticAttribute. This is a special attribute that instructs the CLR to scope any values assigned to or read from the variable to the executing thread, not globally within the AppDomain. This means that if two different threads assign two different values to the same thread static variable, one value will not overwrite the other, and each thread will see the value they assigned to the variable, separately to any other thread. This is a very useful function that allows for ConcurrentBag's concurrency properties. You can think of a thread static variable: [ThreadStatic] private static int m_Value; as doing the same as: private static Dictionary<Thread, int> m_Values; where the executing thread's identity is used to automatically set and retrieve the corresponding value in the dictionary. In .NET 4, this usage of ThreadStaticAttribute is encapsulated in the ThreadLocal class. Lists of lists ConcurrentBag, at its core, operates as a linked list of linked lists: Each outer list node is an instance of ThreadLocalList, and each inner list node is an instance of Node. Each outer ThreadLocalList is owned by a particular thread, accessible through the thread local m_locals variable: private ThreadLocal<ThreadLocalList<T>> m_locals It is important to note that, although the m_locals variable is thread-local, that only applies to accesses through that variable. The objects referenced by the thread (each instance of the ThreadLocalList object) are normal heap objects that are not specific to any thread. Thinking back to the Dictionary analogy above, if each value stored in the dictionary could be accessed by other means, then any thread could access the value belonging to other threads using that mechanism. Only reads and writes to the variable defined as thread-local are re-routed by the CLR according to the executing thread's identity. So, although m_locals is defined as thread-local, the m_headList, m_nextList and m_tailList variables aren't. This means that any thread can access all the thread local lists in the collection by doing a linear search through the outer linked list defined by these variables. Adding items So, onto the collection operations. First, adding items. This one's pretty simple. If the current thread doesn't already own an instance of ThreadLocalList, then one is created (or, if there are lists owned by threads that have stopped, it takes control of one of those). Then the item is added to the head of that thread's list. That's it. Don't worry, it'll get more complicated when we account for the other operations on the list! Taking & Peeking items This is where it gets tricky. If the current thread's list has items in it, then it peeks or removes the head item (not the tail item) from the local list and returns that. However, if the local list is empty, it has to go and steal another item from another list, belonging to a different thread. It iterates through all the thread local lists in the collection using the m_headList and m_nextList variables until it finds one that has items in it, and it steals one item from that list. Up to this point, the two threads had been operating completely independently. To steal an item from another thread's list, the stealing thread has to do it in such a way as to not step on the owning thread's toes. Recall how adding and removing items both operate on the head of the thread's linked list? That gives us an easy way out - a thread trying to steal items from another thread can pop in round the back of another thread's list using the m_tail variable, and steal an item from the back without the owning thread knowing anything about it. The owning thread can carry on completely independently, unaware that one of its items has been nicked. However, this only works when there are at least 3 items in the list, as that guarantees there will be at least one node between the owning thread performing operations on the list head and the thread stealing items from the tail - there's no chance of the two threads operating on the same node at the same time and causing a race condition. If there's less than three items in the list, then there does need to be some synchronization between the two threads. In this case, the lock on the ThreadLocalList object is used to mediate access to a thread's list when there's the possibility of contention. Thread synchronization In ConcurrentBag, this is done using several mechanisms: Operations performed by the owner thread only take out the lock when there are less than three items in the collection. With three or greater items, there won't be any conflict with a stealing thread operating on the tail of the list. If a lock isn't taken out, the owning thread sets the list's m_currentOp variable to a non-zero value for the duration of the operation. This indicates to all other threads that there is a non-locked operation currently occuring on that list. The stealing thread always takes out the lock, to prevent two threads trying to steal from the same list at the same time. After taking out the lock, the stealing thread spinwaits until m_currentOp has been set to zero before actually performing the steal. This ensures there won't be a conflict with the owning thread when the number of items in the list is on the 2-3 item borderline. If any add or remove operations are started in the meantime, and the list is below 3 items, those operations try to take out the list's lock and are blocked until the stealing thread has finished. This allows a thread to steal an item from another thread's list without corrupting it. What about synchronization in the collection as a whole? Collection synchronization Any thread that operates on the collection's global structure (accessing anything outside the thread local lists) has to take out the collection's global lock - m_globalListsLock. This single lock is sufficient when adding a new thread local list, as the items inside each thread's list are unaffected. However, what about operations (such as Count or ToArray) that need to access every item in the collection? In order to ensure a consistent view, all operations on the collection are stopped while the count or ToArray is performed. This is done by freezing the bag at the start, performing the global operation, and unfreezing at the end: The global lock is taken out, to prevent structural alterations to the collection. m_needSync is set to true. This notifies all the threads that they need to take out their list's lock irregardless of what operation they're doing. All the list locks are taken out in order. This blocks all locking operations on the lists. The freezing thread waits for all current lockless operations to finish by spinwaiting on each m_currentOp field. The global operation can then be performed while the bag is frozen, but no other operations can take place at the same time, as all other threads are blocked on a list's lock. Then, once the global operation has finished, the locks are released, m_needSync is unset, and normal concurrent operation resumes. Concurrent principles That's the essence of how ConcurrentBag operates. Each thread operates independently on its own local list, except when they have to steal items from another list. When stealing, only the stealing thread is forced to take out the lock; the owning thread only has to when there is the possibility of contention. And a global lock controls accesses to the structure of the collection outside the thread lists. Operations affecting the entire collection take out all locks in the collection to freeze the contents at a single point in time. So, what principles can we extract here? Threads operate independently Thread-static variables and ThreadLocal makes this easy. Threads operate entirely concurrently on their own structures; only when they need to grab data from another thread is there any thread contention. Minimised lock-taking Even when two threads need to operate on the same data structures (one thread stealing from another), they do so in such a way such that the probability of actually blocking on a lock is minimised; the owning thread always operates on the head of the list, and the stealing thread always operates on the tail. Management of lockless operations Any operations that don't take out a lock still have a 'hook' to force them to lock when necessary. This allows all operations on the collection to be stopped temporarily while a global snapshot is taken. Hopefully, such operations will be short-lived and infrequent. That's all the concurrent collections covered. I hope you've found it as informative and interesting as I have. Next, I'll be taking a closer look at ThreadLocal, which I came across while analyzing ConcurrentBag. As you'll see, the operation of this class deserves a much closer look.

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  • PackageMaker install script for rxtx

    - by vinzenzweber
    I am using PackageMaker to create an installer for my application. During installation I need to run a bash script to properly install rxtx, a JNI library for serial port communication. This library needs to have the directory /var/lock in place with user "root" and group "uucp". The installation script also needs to add the current user to the group "uucp" for the lib to be able to write to /var/lock. Now when I run my application installer the preinstall script is run as root. Therefore "whoami" returns root instead of the user who is actually running the installer. The result is that rxtx is not able to create lock files in /var/lock because the actual user was not added as a member to "uucp". How can I get the user while my script is run by the installer. Or is it better to set the permissions for /var/lock to a different group maybe? Any suggestions are welcome! !/bin/sh curruser=whoami logger "Setting permissions for /var/lock for user $curruser!" if [ ! -d /var/lock ] then logger "Creating /var/lock!" sudo mkdir /var/lock fi sudo chgrp uucp /var/lock sudo chmod 775 /var/lock MacOSX 10.5 and later use dscl if [ sudo dscl . -read /Groups/uucp GroupMembership | grep $curruser | wc -l = "0" ] then logger "Add user $curruser to /Groups/uucp!" sudo dscl . -append /Groups/uucp GroupMembership $curruser # to revert use: # sudo dscl . -delete /Groups/uucp GroupMembership $curruser else logger "GroupMembership of /var/lock not changed!" fi

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  • Problems with Threading in Python 2.5, KeyError: 51, Help debugging?

    - by vignesh-k
    I have a python script which runs a particular script large number of times (for monte carlo purpose) and the way I have scripted it is that, I queue up the script the desired number of times it should be run then I spawn threads and each thread runs the script once and again when its done. Once the script in a particular thread is finished, the output is written to a file by accessing a lock (so my guess was that only one thread accesses the lock at a given time). Once the lock is released by one thread, the next thread accesses it and adds its output to the previously written file and rewrites it. I am not facing a problem when the number of iterations is small like 10 or 20 but when its large like 50 or 150, python returns a KeyError: 51 telling me element doesn't exist and the error it points out to is within the lock which puzzles me since only one thread should access the lock at once and I do not expect an error. This is the class I use: class errorclass(threading.Thread): def __init__(self, queue): self.__queue=queue threading.Thread.__init__(self) def run(self): while 1: item = self.__queue.get() if item is None: break result = myfunction() lock = threading.RLock() lock.acquire() ADD entries from current thread to entries in file and REWRITE FILE lock.release() queue = Queue.Queue() for i in range(threads): errorclass(queue).start() for i in range(desired iterations): queue.put(i) for i in range(threads): queue.put(None) Python returns with KeyError: 51 for large number of desired iterations during the adding/write file operation after lock access, I am wondering if this is the correct way to use the lock since every thread has a lock operation rather than every thread accessing a shared lock? What would be the way to rectify this?

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  • Error when try to install subversion on linux [closed]

    - by Juan Carlos Vega Neira
    Possible Duplicate: Fixing Could not get lock /var/lib/dpkg/lock I have installed Ubuntu server 11.10 and after the installation finishes I installed apache server by this code. sudo apt-get install apache2 Then I tried to install subversion by this code: sudo apt-get install subversion as I saw on some blogs and got this error: E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it? How can I solve this error?

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  • Upgrading Sharepoint MOSS 2007 Farm to Sharepoint 2010 "waiting to get a lock to upgrade the farm"

    - by Wes Weeks
    My first inplace upgrade of a MOSS 2007 farm to sharepoint went pretty smooth. I read the preupgrade documentation and was comfortable with the steps.  Since it was a fairly new installation of Moss changes were minimal and I wasn't anticipating too many problems The one issue I got was after installing the software on all of the farm.  I went to the first machine which ran Sharepoint 2010 central administration and ran the Sharepoint 2010 Products Configuration Wizard.  I received the message that I would need to run the configuration on each server in the farm.  Fair enough, I expected as much. The wizard completed without issue on the first server, but when I tried to run it on the others it hung with a "waiting to get a lock to upgrade the farm" message.  It hung for about 10 minutes and then the wizard failed.  Did a few searches on Google and Bing and got 0 results for that message.  None, Nothing, Zilch.  I'm on my own... For grins, hit the help button on the configuration wizard and it seemed to indicate that the configuration wizard needed to be run on all farm servers simultaneously.  I started it again on the first server to the point I got the message about needing to be run on all servers on the farm and then started the wizard on the other servers and ran it to that point as well.  I then clicked ok on the first server and then the subsuquent servers. It took a while and it did hang on the lock message for some time, but then it did kick off and completed succesfully on all of them.  Yeah! Hope this helps someone else!  Now there should be at least one post with this error message on it!

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  • How to prevent samba from holding a file lock after a client disconnects?

    - by Jean-Francois Chevrette
    Here I have a Samba server (Debian 5.0) thats is configured to host Windows XP profiles. Clients connects to this server and work on their profiles directly on the samba share (the profile is not copied locally). Every now and then, a client may not shutdown properly and thus Windows does not free the file locks. When looking at the samba locking table, we can see that many files are still locked even though the client is not connected anymore. In our case, this seems to occur with lockfiles created by Mozilla Thunderbird and Firefox. Here's an example of the samba locking table: # smbstatus -L | grep DENY_ALL | head -n5 Pid Uid DenyMode Access R/W Oplock SharePath Name Time -------------------------------------------------------------------------------------------------- 15494 10345 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user1 app.profile/user1.thunderbird/parent.lock Mon Nov 22 07:12:45 2010 18040 10454 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user2 app.profile/user2.thunderbird/parent.lock Mon Nov 22 11:20:45 2010 26466 10056 DENY_ALL 0x3019f RDWR EXCLUSIVE+BATCH /home/CORP/user3 app.profile/user3.firefox/parent.lock Mon Nov 22 08:48:23 2010 We can see that the files were opened by Windows and imposed a DENY_ALL lock. Now when a client reconnects to this share and tries to open those files, samba says that they are locked and denies access. Is there any way to work around this situation or am I missing something? Edit: We would like to avoid disabling file locks on the samba server because there are good reasons to have those enabled.

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  • Know more about Enqueue Deadlock Detection

    - by Liu Maclean(???)
    ??? ORACLE ALLSTAR???????????????????,??????? ???????enqueue lock?????????3 ??????,????????????????????????????ora-00060 dead lock??process???3s: SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi PL/SQL Release 10.2.0.5.0 - Production CORE 10.2.0.5.0 Production TNS for Linux: Version 10.2.0.5.0 - Production NLSRTL Version 10.2.0.5.0 - Production SQL> select * from global_name; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com PROCESS A: set timing on; update maclean1 set t1=t1+1; PROCESS B: update maclean2 set t1=t1+1; PROCESS A: update maclean2 set t1=t1+1; PROCESS B: update maclean1 set t1=t1+1; ??3s? PROCESS A ?? ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:03.02 ????Process A????????????? 3s,?????????????,??????? ?????????? ???????: SQL> col name for a30 SQL> col value for a5 SQL> col DESCRIB for a50 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm='_enqueue_deadlock_scan_secs'; NAME VALUE DESCRIB ------------------------------ ----- -------------------------------------------------- _enqueue_deadlock_scan_secs 0 deadlock scan interval SQL> alter system set "_enqueue_deadlock_scan_secs"=18 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. PROCESS A: SQL> set timing on; SQL> update maclean1 set t1=t1+1; 1 row updated. Elapsed: 00:00:00.06 Process B SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Process A: SQL> SQL> alter session set events '10704 trace name context forever,level 10:10046 trace name context forever,level 8'; Session altered. SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource  Elapsed: 00:00:18.05 ksqcmi: TX,90011,4a9 mode=6 timeout=21474836 WAIT #12: nam='enq: TX - row lock contention' ela= 2930070 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114759849120 WAIT #12: nam='enq: TX - row lock contention' ela= 2930636 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114762779801 WAIT #12: nam='enq: TX - row lock contention' ela= 2930439 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114765710430 *** 2012-06-12 09:58:43.089 WAIT #12: nam='enq: TX - row lock contention' ela= 2931698 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114768642192 WAIT #12: nam='enq: TX - row lock contention' ela= 2930428 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114771572755 WAIT #12: nam='enq: TX - row lock contention' ela= 2931408 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114774504207 DEADLOCK DETECTED ( ORA-00060 ) [Transaction Deadlock] The following deadlock is not an ORACLE error. It is a deadlock due to user error in the design of an application or from issuing incorrect ad-hoc SQL. The following information may aid in determining the deadlock: ??????Process A?’enq: TX – row lock contention’ ?????ORA-00060 deadlock detected????3s ??? 18s , ???hidden parameter “_enqueue_deadlock_scan_secs”?????,????????0? ??????????: SQL> alter system set "_enqueue_deadlock_scan_secs"=4 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> alter system set "_enqueue_deadlock_time_sec"=9 scope=spfile; System altered. Elapsed: 00:00:00.00 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 SQL> set timing on SQL> select * from maclean1 for update wait 8; T1 ---------- 11 Elapsed: 00:00:00.01 PROCESS B SQL> select * from maclean2 for update wait 8; T1 ---------- 3 SQL> select * from maclean1 for update wait 8; select * from maclean1 for update wait 8 PROCESS A SQL> select * from maclean2 for update wait 8; select * from maclean2 for update wait 8 * ERROR at line 1: ORA-30006: resource busy; acquire with WAIT timeout expired Elapsed: 00:00:08.00 ???????? ??? select for update wait?enqueue request timeout ?????8s? ,???????”_enqueue_deadlock_scan_secs”=4(deadlock scan interval),?4s???deadlock detected,????Process A????deadlock ???, ??????? ??Process A?????8s?raised??”ORA-30006: resource busy; acquire with WAIT timeout expired”??,??ORA-00060,?????process A???????? ????????”_enqueue_deadlock_time_sec”(requests with timeout <= this will not have deadlock detection)???,?enqueue request time < “_enqueue_deadlock_time_sec”?Server process?????dead lock detection,?????????enqueue request ??????timeout??????(_enqueue_deadlock_time_sec????5,?timeout<5s),???????????????;??????timeout>”_enqueue_deadlock_time_sec”???,Oracle????????????????????? ??????????: SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 Process A: SQL> set timing on; SQL> select * from maclean1 for update wait 10; T1 ---------- 11 Process B: SQL> select * from maclean2 for update wait 10; T1 ---------- 3 SQL> select * from maclean1 for update wait 10; PROCESS A: SQL> select * from maclean2 for update wait 10; select * from maclean2 for update wait 10 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:06.02 ??????? select for update wait 10?10s??, ?? 10s?????_enqueue_deadlock_time_sec???(9s),??Process A???????? ???????????????6s ???????_enqueue_deadlock_scan_secs?4s ? ???????????,???????????_enqueue_deadlock_scan_secs?????????3???? ??: enqueue lock?????????????? 1. ?????????deadlock detection??3s????, ????????_enqueue_deadlock_scan_secs(deadlock scan interval)???,??????0,????????_enqueue_deadlock_scan_secs?????????3???, ?_enqueue_deadlock_scan_secs=0 ??3s??, ?_enqueue_deadlock_scan_secs=4??6s??,????? 2. ???????_enqueue_deadlock_time_sec(requests with timeout <= this will not have deadlock detection)???,?enqueue request timeout< _enqueue_deadlock_time_sec(????5),?Server process?????????enqueue request timeout>_enqueue_deadlock_time_sec ????_enqueue_deadlock_scan_secs???????, ??request timeout??????select for update wait [TIMEOUT]??? ??: ???10.2.0.1?????????2?hidden parameter , ???patchset 10.2.0.3????? _enqueue_deadlock_time_sec, ?patchset 10.2.0.5??????_enqueue_deadlock_scan_secs? ?????RAC???????????10s, ???????_lm_dd_interval(dd time interval in seconds) ,????????8.0.6???? ???????????????,??????,  ?10g???????60s,?11g???????10s?  ???????11g??_lm_dd_interval?????????????,?????11g??LMD????????????,??????????RAC?LMD?Deadlock Detection???????CPU,???11g?Oracle????Team???LMD????????CPU????: ????????11g?LMD???????,???????11g??? UTS TRACE ????? DD???: SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production PL/SQL Release 11.2.0.3.0 - Production CORE 11.2.0.3.0 Production TNS for Linux: Version 11.2.0.3.0 - Production NLSRTL Version 11.2.0.3.0 - Production SQL> SQL> select * from global_name 2 ; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com SQL> alter system set "_lm_dd_interval"=20 scope=spfile; System altered. SQL> startup force; ORACLE instance started. Total System Global Area 1570009088 bytes Fixed Size 2228704 bytes Variable Size 1325403680 bytes Database Buffers 234881024 bytes Redo Buffers 7495680 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter lm_dd NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _lm_dd_interval integer 20 SQL> select count(*) from gv$instance; COUNT(*) ---------- 2 instance 1: SQL> oradebug setorapid 12 Oracle pid: 12, Unix process pid: 8608, image: [email protected] (LMD0) ? LMD0??? UTS TRACE??RAC???????????? SQL> oradebug event 10046 trace name context forever,level 8:10708 trace name context forever,level 103: trace[rac.*] disk high; Statement processed. Elapsed: 00:00:00.00 SQL> update maclean1 set t1=t1+1; 1 row updated. instance 2: SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Instance 1: SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:20.51 LMD0???UTS TRACE 2012-06-12 22:27:00.929284 : [kjmpbmsg:process][type 22][msg 0x7fa620ac85a8][from 1][seq 8148.0][len 192] 2012-06-12 22:27:00.929346 : [kjmxmpm][type 22][seq 0.0][msg 0x7fa620ac85a8][from 1] *** 2012-06-12 22:27:00.929 * kjddind: received DDIND msg with subtype x6 * reqp->dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: 2012-06-12 22:27:00.929346*: kjddind: req->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: >> DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929346*: lock [0x95023930,829], op = [mast] 2012-06-12 22:27:00.929346*: reqp->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_REMOTE 2012-06-12 22:27:00.929346*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopr[TX 0xe000c.0x32][ext 0x5,0x0]: blocking lock 0xbbb9a800, owner 2097154 of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopt: converting lock 0xbbce92f8 on 'TX' 0x80016.0x5d4,txid [2097154,34]of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929855 : GSIPC:AMBUF: rcv buff 0x7fa620aa8cd8, pool rcvbuf, rqlen 1102 2012-06-12 22:27:00.929878 : GSIPC:GPBMSG: new bmsg 0x7fa620aa8d48 mb 0x7fa620aa8cd8 msg 0x7fa620aa8d68 mlen 192 dest x100 flushsz -1 2012-06-12 22:27:00.929878*: << DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 2->1,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929878*: lock [0xbbce92f8,287], op = [mast] 2012-06-12 22:27:00.929878*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929923 : [kjmpbmsg:compl][msg 0x7fa620ac8588][typ p][nmsgs 1][qtime 0][ptime 0] 2012-06-12 22:27:00.929947 : GSIPC:PBAT: flush start. flag 0x79 end 0 inc 4.4 2012-06-12 22:27:00.929963 : GSIPC:PBAT: send bmsg 0x7fa620aa8d48 blen 224 dest 1.0 2012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 2012-06-12 22:27:00.929996 : GSIPC:BSEND: flushing sndq 0xb491dd28, id 0, dcx 0xbc517770, inst 1, rcvr 0 qlen 0 1 2012-06-12 22:27:00.930014 : GSIPC:BSEND: no batch1 msg 0x7fa620aa8d48 type 65521 len 224 dest (1:0) 2012-06-12 22:27:00.930088 : kjbsentscn[0x0.3f72dc][to 1] 2012-06-12 22:27:00.930144 : GSIPC:SENDM: send msg 0x7fa620aa8d48 dest x10000 seq 8325 type 65521 tkts x1 mlen xe00110 2012-06-12 22:27:00.930531 : GSIPC:KSXPCB: msg 0x7fa620aa8d48 status 30, type 65521, dest 1, rcvr 0 WAIT #0: nam='ges remote message' ela= 1372 waittime=80 loop=0 p3=74 obj#=-1 tim=1339554420931640 2012-06-12 22:27:00.931728 : GSIPC:RCVD: ksxp msg 0x7fa620af6490 sndr 1 seq 0.8149 type 65521 tkts 1 2012-06-12 22:27:00.931746 : GSIPC:RCVD: watq msg 0x7fa620af6490 sndr 1, seq 8149, type 65521, tkts 1 2012-06-12 22:27:00.931763 : GSIPC:RCVD: seq update (0.8148)->(0.8149) tp -15 fg 0x4 from 1 pbattr 0x0 2012-06-12 22:27:00.931779 : GSIPC:TKT: collect msg 0x7fa620af6490 from 1 for rcvr 0, tickets 1 2012-06-12 22:27:00.931794 : kjbrcvdscn[0x0.3f72dc][from 1][idx 2012-06-12 22:27:00.931810 : kjbrcvdscn[no bscn dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 2012-06-12 22:27:00.932058*: kjddind: req->timestamp [0.15], kjddt [0.15] 2012-06-12 22:27:00.932058*: >> DDmsg:KJX_DD_VALIDATE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.932058*: lock [(nil),0], op = [vald_dd] 2012-06-12 22:27:00.932058*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_VALIDATE *** 2012-06-12 22:27:00.932 * kjddvald called: kjxmddi stuff: * cont_lockp (nil) * dd_lockp 0x95023930 * dd_inst 1 * dd_master_inst 1 * sgh graph: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 POP WFG NODE: lock=(nil) * kjddvald: dump the PRQ: BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 * kjddvald: KJDD_NXTONOD ->node_kjddsg.dinst_kjddnd =1 * kjddvald: ... which is not my node, my subgraph is validated but the cycle is not complete Global blockers dump start:--------------------------------- DUMP LOCAL BLOCKER/HOLDER: block level 5 res [0x80016][0x5d4],[TX][ext 0x2,0x0] ??dead lock!!! ???????11.2.0.3???? RAC LMD???????????”_lm_dd_interval”????????????20s?  ???????10g?_lm_dd_interval???60s,??????Processes?????????????????,????????????Server Process????????60s??????11g?????(??????LMD???????)???????,???????????10s??? Enqueue Deadlock Detection? ?11g??? RAC?LMD???????hidden parameter ????”_lm_dd_interval”???,RAC????????????????,???????????: SQL> col name for a50 SQL> col describ for a60 SQL> col value for a20 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm like '_lm_dd%'; NAME VALUE DESCRIB -------------------------------------------------- -------------------- ------------------------------------------------------------ _lm_dd_interval 20 dd time interval in seconds _lm_dd_scan_interval 5 dd scan interval in seconds _lm_dd_search_cnt 3 number of dd search per token get _lm_dd_max_search_time 180 max dd search time per token _lm_dd_maxdump 50 max number of locks to be dumped during dd validation _lm_dd_ignore_nodd FALSE if TRUE nodeadlockwait/nodeadlockblock options are ignored 6 rows selected.

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  • .NET Code Evolution

    - by Alois Kraus
    Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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  • Utility that helps in file locking - expert tips wanted

    - by maix
    I've written a subclass of file that a) provides methods to conveniently lock it (using fcntl, so it only supports unix, which is however OK for me atm) and b) when reading or writing asserts that the file is appropriately locked. Now I'm not an expert at such stuff (I've just read one paper [de] about it) and would appreciate some feedback: Is it secure, are there race conditions, are there other things that could be done better … Here is the code: from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN, LOCK_NB class LockedFile(file): """ A wrapper around `file` providing locking. Requires a shared lock to read and a exclusive lock to write. Main differences: * Additional methods: lock_ex, lock_sh, unlock * Refuse to read when not locked, refuse to write when not locked exclusivly. * mode cannot be `w` since then the file would be truncated before it could be locked. You have to lock the file yourself, it won't be done for you implicitly. Only you know what lock you need. Example usage:: def get_config(): f = LockedFile(CONFIG_FILENAME, 'r') f.lock_sh() config = parse_ini(f.read()) f.close() def set_config(key, value): f = LockedFile(CONFIG_FILENAME, 'r+') f.lock_ex() config = parse_ini(f.read()) config[key] = value f.truncate() f.write(make_ini(config)) f.close() """ def __init__(self, name, mode='r', *args, **kwargs): if 'w' in mode: raise ValueError('Cannot open file in `w` mode') super(LockedFile, self).__init__(name, mode, *args, **kwargs) self.locked = None def lock_sh(self, **kwargs): """ Acquire a shared lock on the file. If the file is already locked exclusively, do nothing. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ if self.locked == 'ex': return # would implicitly remove the exclusive lock return self._lock(LOCK_SH, **kwargs) def lock_ex(self, **kwargs): """ Acquire an exclusive lock on the file. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ return self._lock(LOCK_EX, **kwargs) def unlock(self): """ Release all locks on the file. Flushes if there was an exclusive lock. :returns: Lock status from before the call (one of 'sh', 'ex', None). """ if self.locked == 'ex': self.flush() return self._lock(LOCK_UN) def _lock(self, mode, nonblocking=False): flock(self, mode | bool(nonblocking) * LOCK_NB) before = self.locked self.locked = {LOCK_SH: 'sh', LOCK_EX: 'ex', LOCK_UN: None}[mode] return before def _assert_read_lock(self): assert self.locked, "File is not locked" def _assert_write_lock(self): assert self.locked == 'ex', "File is not locked exclusively" def read(self, *args): self._assert_read_lock() return super(LockedFile, self).read(*args) def readline(self, *args): self._assert_read_lock() return super(LockedFile, self).readline(*args) def readlines(self, *args): self._assert_read_lock() return super(LockedFile, self).readlines(*args) def xreadlines(self, *args): self._assert_read_lock() return super(LockedFile, self).xreadlines(*args) def __iter__(self): self._assert_read_lock() return super(LockedFile, self).__iter__() def next(self): self._assert_read_lock() return super(LockedFile, self).next() def write(self, *args): self._assert_write_lock() return super(LockedFile, self).write(*args) def writelines(self, *args): self._assert_write_lock() return super(LockedFile, self).writelines(*args) def flush(self): self._assert_write_lock() return super(LockedFile, self).flush() def truncate(self, *args): self._assert_write_lock() return super(LockedFile, self).truncate(*args) def close(self): self.unlock() return super(LockedFile, self).close() (the example in the docstring is also my current use case for this) Thanks for having read until down here, and possibly even answering :)

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  • Windows 7: Screen will power of, or blank and lock, but not both.

    - by Heptite
    For some reason, my Windows 7 (Ultimate, 64bit) laptop will not power off the display and keep it off if I have the screen saver and/or the timed auto-lock enabled. Either the display blanks (and locks) but never powers off, or it powers off for less then a minute, then the back light visibly powers back on and stays on, even though the screen remains blanked until I touch a key or the trackpad. I've tried varying the screen power down time to greater than, less than, and exactly equal to the blank screen/lock time, with no success. Turning the screen saver and the timed auto-lock off does allow the timed display power down in the power settings to work properly. (Note that I am not talking about system sleep or hibernate. I'm talking about when the machine remains running, but only the display should power down.)

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  • Xen domain migration locking problem

    - by brodie
    I am trying to live migrate a VM (domain) between two Xen servers. I have xen locking (xend-domain-lock = yes) configured with a ocfs2 shared storage between them. This locking is working fine. If I try to start up the VM on the secondary server it refuses to start (which is correct). The problem I am having is when trying to do live migration, it seems like it is trying to remove the lock twice. The first lock it removes is for "domain test", the second is for "migrating-test" which does not exist. Should their be a lock for this "migrating-test" VM? These are the relevant options in the xen config file: (xend-relocation-server yes) (xend-relocation-port 8002) (xend-relocation-address '') (xend-relocation-hosts-allow '') (xend-domain-lock yes) (xend-domain-lock-path /var/lib/xen/lock) This is the section of the log: [2010-06-10 10:45:57 14488] DEBUG (XendDomainInfo:4054) Releasing lock for domain test [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) SUSPEND shinfo 000c6ceb [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) delta 21ms, dom0 95%, target 0%, sent 57Mb/s, dirtied 173Mb/s 111 pages 4: sent 111, skipped 0, delta 6ms, dom0 100%, target 0%, sent 606Mb/s, dirtied 606Mb/s 111 pages [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) Total pages sent= 131295 (0.99x) [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) (of which 0 were fixups) [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) All memory is saved [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) Save exit rc=0 [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:123) Domain 22 suspended. [2010-06-10 10:45:57 14488] DEBUG (XendDomainInfo:2757) XendDomainInfo.destroy: domid=22 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2227) Destroying device model [2010-06-10 10:45:58 14488] INFO (image:567) migrating-test device model terminated [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2234) Releasing devices [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vif/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vif, device = vif/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vkbd/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vkbd, device = vkbd/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing console/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = console, device = console/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vbd/51712 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vbd, device = vbd/51712 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vfb/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vfb, device = vfb/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:4054) Releasing lock for domain migrating-test [2010-06-10 10:45:59 14488] ERROR (XendDomainInfo:4070) Failed to remove unmanaged directory /var/lib/xen/lock/b01515ae-9173-03cb-0cb7-06f3dfbede8b.

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  • Windows 7: Screen will power off, or blank and lock, but not both.

    - by Heptite
    For some reason, my Windows 7 (Ultimate, 64bit) laptop will not power off the display and keep it off if I have the screen saver and/or the timed auto-lock enabled. Either the display blanks (and locks) but never powers off, or it powers off for less then a minute, then the back light visibly powers back on and stays on, even though the screen remains blanked until I touch a key or the trackpad. I've tried varying the screen power down time to greater than, less than, and exactly equal to the blank screen/lock time, with no success. Turning the screen saver and the timed auto-lock off does allow the timed display power down in the power settings to work properly. (Note that I am not talking about system sleep or hibernate. I'm talking about when the machine remains running, but only the display should power down.)

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  • Windows 8: How to Lock (not sleep) laptop on lid close?

    - by Eye of Hell
    If my laptop is connected to power source and is not configured to sleep on lid close (it is connected to power source and is working, i don't want it to sleep. It's compiling my code) if i close the lid, laptop will do nothing. This works as expected, but actually if i have my laptop connected to power source in the office it will be good to lock it if i close a lid. So no one can just open the lid and see my unlocked desktop. I searched google and it says thet correct use case is to manually lock laptop via Win + L every time before lid is closed. This is ok, but not very secure - after all, i can forget Win + L. Is t any easy way (maybe some registry value or app) to configure windows laptop so it will lock on lid close even without sleep? Of course i can write app / powershell script for this task, but this is not suitable for non-programmers end users.

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  • Does learning to develop for iOS create a lock-in?

    - by Jungle Hunter
    If I begin my career (first job) with developing on the iOS platform, does that lock me in into iOS and Mac OS X development only? By locking me in I mean will that create barriers for me to switch technologies as I would be mainly working with Objective-C. If yes, does that make my career choices limited? I'm interested in comparing this with Android development, which if pursued will leave me with Java skills (correct me if I'm wrong) which I can use elsewhere.

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  • Is there any way to lock down Photoshop to prevent designers from creating styles that cannot be rendered in CSS?

    - by Hugo Rodger-Brown
    Photoshop is a much more powerful design tool than CSS, and given free reign to design at will, designers will often tweak things like font settings to a degree that cannot be recreated on the web. Is there any way to lock down Photoshop, or perhaps run an equivalent of the Office 2010 "Compatability report" that shows the designer where they have designed something that cannot be rendered on a web page. Something like the old-school "web-safe" colour palette, but for an overall design.

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  • HTG Explains: What Are the Sys Rq, Scroll Lock, and Pause/Break Keys on My Keyboard?

    - by Chris Hoffman
    Glance at your keyboard and chances are you’ll see a few keys you never use near the top-right corner – Sys Rq, Scroll Lock, and Pause / Break. Have you ever wondered what those keys are for? While these keys have been removed from some computer keyboards today, they’re still a common sight — even on new keyboards. Image Credit: ajmexico on Flickr 8 Deadly Commands You Should Never Run on Linux 14 Special Google Searches That Show Instant Answers How To Create a Customized Windows 7 Installation Disc With Integrated Updates

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  • When multitasking a fullscreen app, cant get mouse to lock back in the application: Ex. SPAZ game

    - by NikhilWanpal
    When I am running a fullscreen application, for example the game SPAZ from the HumbleBundle 6, if some popup comes or if I press the super key to come back to desktop and minimize the game, I am unable to play the game again. The game just wont lock my mouse again, I am sometimes able to get it to become fullscreen again (no idea exactly how!), but the mouse just wont get locked.. Any idea how to continue the game without exit and restart?

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