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• Ruby. Mongoid. Relations

  - by Scepion1d

  I've encountered some problems with MongoID. I have three models: require 'mongoid' class Configuration include Mongoid::Document belongs_to :user field :links, :type => Array field :root, :type => String field :objects, :type => Array field :categories, :type => Array has_many :entries end class TimeDim include Mongoid::Document field :day, :type => Integer field :month, :type => Integer field :year, :type => Integer field :day_of_week, :type => Integer field :minute, :type => Integer field :hour, :type => Integer has_many :entries end class Entry include Mongoid::Document belongs_to :configuration belongs_to :time_dim field :category, :type => String # any other dynamic fields end Creating documents for Configurations and TimeDims is successful. But when i've trying to execute following code: params = Hash.new params[:configuration] = config # an instance of Configuration from DB entry.each do |key, value| params[key.to_sym] = value # String end unless Entry.exists?(conditions: params) params[:time_dim] = self.generate_time_dim # an instance of TimeDim from DB params[:category] = self.detect_category(descr) # String Entry.new(params).save end ... i saw following output: /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/bson-1.6.1/lib/bson/bson_c.rb:24:in `serialize': Cannot serialize an object of class Configuration into BSON. (BSON::InvalidDocument) from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/bson-1.6.1/lib/bson/bson_c.rb:24:in `serialize' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/cursor.rb:604:in `construct_query_message' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/cursor.rb:465:in `send_initial_query' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/cursor.rb:458:in `refresh' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/cursor.rb:128:in `next' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/db.rb:509:in `command' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongo-1.6.1/lib/mongo/cursor.rb:191:in `count' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/cursor.rb:42:in `block in count' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/collections/retry.rb:29:in `retry_on_connection_failure' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/cursor.rb:41:in `count' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/contexts/mongo.rb:93:in `count' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/criteria.rb:45:in `count' from /home/scepion1d/Workspace/RubyMine/dana-x/.bundle/ruby/1.9.1/gems/mongoid-2.4.6/lib/mongoid/finders.rb:60:in `exists?' from /home/scepion1d/Workspace/RubyMine/dana-x/crawler/crawler.rb:110:in `block (2 levels) in push_entries_to_db' from /home/scepion1d/Workspace/RubyMine/dana-x/crawler/crawler.rb:103:in `each' from /home/scepion1d/Workspace/RubyMine/dana-x/crawler/crawler.rb:103:in `block in push_entries_to_db' from /home/scepion1d/Workspace/RubyMine/dana-x/crawler/crawler.rb:102:in `each' from /home/scepion1d/Workspace/RubyMine/dana-x/crawler/crawler.rb:102:in `push_entries_to_db' from main_starter.rb:15:in `<main>' Can anyone tell what am I doing wrong?

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• Extjs4: editable rowbody

  - by peter

  in my first ExtJs4 project i use a editable grid with the feature rowbody to have a big textfield displayed under each row. I want it to be editable on a dblclick. I succeeded in doing so by replacing the innerHTML of the rowbody by a textarea but the special keys don't do what they are supposed to do (move the cursor). If a use the textarea in a normal field i don't have this probem. Same problem in IE7 and FF4 gridInfo = Ext.create('Ext.ux.LiveSearchGridPanel', { id: 'gridInfo', height: '100%', width: '100%', store: storeInfo, columnLines: true, selType: 'cellmodel', columns: [ {text: "Titel", flex: 1, dataIndex: 'titel', field:{xtype:'textfield'}}, {text: "Tags", id: "tags", flex: 1, dataIndex: 'tags', field:{xtype:'textfield'}}, {text: "Hits", dataIndex: 'hits'}, {text: "Last Updated", renderer: Ext.util.Format.dateRenderer('d/m/Y'), dataIndex: 'lastChange'} ], plugins: [ Ext.create('Ext.grid.plugin.CellEditing', { clicksToEdit: 1 }) ], features: [ { ftype: 'rowbody', getAdditionalData: function(data, idx, record, orig) { var headerCt = this.view.headerCt, colspan = headerCt.getColumnCount(); return { rowBody: data.desc, //the big textfieldvalue, can't use a textarea here 8< rowBodyCls: this.rowBodyCls, rowBodyColspan: colspan }; } }, {ftype: 'rowwrap'} ] }); me.on('rowbodydblclick', function(gridView, el, event, o) { ... rb = td.down('.x-grid-rowbody').dom; var value = rb.innerText?rb.innerText:rb.textContent; rb.innerHTML = ''; Ext.create('Ext.form.field.TextArea', { id: 'textarea1', value : value, renderTo: rb, border: false, enterIsSpecial: true, enableKeyEvents: true, disableKeyFilter: true, listeners: { 'blur': function(el, o) { rb.innerHTML = el.value; }, 'specialkey': function(field, e){ console.log(e.keyCode); //captured but nothing happens } } }).show(); damn, can't publish my own solution, looks like somebody else has to answer, anyway, here is the function that works function editDesc(me, gridView, el, event, o) { var width = Ext.fly(el).up('table').getWidth(); var rb = event.target; var value = rb.innerText?rb.innerText:rb.textContent; rb.innerHTML = '' var txt = Ext.create('Ext.form.field.TextArea', { value : value, renderTo: rb, border: false, width: width, height: 300, enterIsSpecial: true, disableKeyFilter: true, listeners: { 'blur': function(el, o) { var value = el.value.replace('\n','<br>') rb.innerHTML = value; }, 'specialkey': function(field, e){ e.stopPropagation(); } } }); var txtTextarea = Ext.fly(rb).down('textarea'); txtTextarea.dom.style.color = 'blue'; txtTextarea.dom.style.fontSize = '11px'; } Hi Molecule Man, as an alternative to the approach above i tried the Ext.Editor. It works but i want it inline but when i render it to the rowbody, the field blanks and i have no editor, any ideas ? gridInfo = Ext.create('Ext.grid.Panel', { id: 'gridInfo', height: '100%', width: '100%', store: storeInfo, columnLines: true, selType: 'cellmodel', viewConfig: {stripeRows: false, trackOver: true}, columns: [ {text: "Titel", flex: 1, dataIndex: 'titel', field:{xtype:'textfield'}}, ... {text: "Last Updated", renderer: Ext.util.Format.dateRenderer('d/m/Y'), dataIndex: 'lastChange'} ], plugins: [ Ext.create('Ext.grid.plugin.CellEditing', { clicksToEdit: 1 }) ], features: [ { ftype: 'rowbody', getAdditionalData: function(data, idx, record, orig) { var headerCt = this.view.headerCt, colspan = headerCt.getColumnCount(); return { rowBody: data.desc, rowBodyCls: this.rowBodyCls, rowBodyColspan: colspan }; } } ], listeners:{ rowbodyclick: function(gridView, el, event) { //werkt editDesc(this, gridView, el, event); } } }); function editDesc(me, gridView, el, event, o) { var rb = event.target; me.txt = new Ext.Editor({ field: {xtype: 'textarea'}, updateEl: true, cancelOnEsc: true, floating: true, renderTo: rb //when i do this, the field becomes empty and i don't get the editor }); me.txt.startEdit(el); }

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• What is correct HTTP status code when redirecting to a login page?

  - by PHP_Jedi

  When a user is not logged in and tries to access an page that requires login, what is the correct HTTP status code for a redirect to the login page? I don't feel that any of the 3xx fit that description. 10.3.1 300 Multiple Choices The requested resource corresponds to any one of a set of representations, each with its own specific location, and agent- driven negotiation information (section 12) is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that location. Unless it was a HEAD request, the response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content- Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection. If the server has a preferred choice of representation, it SHOULD include the specific URI for that representation in the Location field; user agents MAY use the Location field value for automatic redirection. This response is cacheable unless indicated otherwise. 10.3.2 301 Moved Permanently The requested resource has been assigned a new permanent URI and any future references to this resource SHOULD use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise. The new permanent URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued. Note: When automatically redirecting a POST request after receiving a 301 status code, some existing HTTP/1.0 user agents will erroneously change it into a GET request. 10.3.3 302 Found The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field. The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). If the 302 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued. Note: RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request. However, most existing user agent implementations treat 302 as if it were a 303 response, performing a GET on the Location field-value regardless of the original request method. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected of the client. 10.3.4 303 See Other The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable. The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). Note: Many pre-HTTP/1.1 user agents do not understand the 303 status. When interoperability with such clients is a concern, the 302 status code may be used instead, since most user agents react to a 302 response as described here for 303. 10.3.5 304 Not Modified If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields. The response MUST include the following header fields: - Date, unless its omission is required by section 14.18.1 If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without one (as already specified by [RFC 2068], section 14.19), caches will operate correctly. - ETag and/or Content-Location, if the header would have been sent in a 200 response to the same request - Expires, Cache-Control, and/or Vary, if the field-value might differ from that sent in any previous response for the same variant If the conditional GET used a strong cache validator (see section 13.3.3), the response SHOULD NOT include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. If a 304 response indicates an entity not currently cached, then the cache MUST disregard the response and repeat the request without the conditional. If a cache uses a received 304 response to update a cache entry, the cache MUST update the entry to reflect any new field values given in the response. 10.3.6 305 Use Proxy The requested resource MUST be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses MUST only be generated by origin servers. Note: RFC 2068 was not clear that 305 was intended to redirect a single request, and to be generated by origin servers only. Not observing these limitations has significant security consequences. 10.3.7 306 (Unused) The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved. 10.3.8 307 Temporary Redirect The requested resource resides temporarily under a different URI. Since the redirection MAY be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field. The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s) , since many pre-HTTP/1.1 user agents do not understand the 307 status. Therefore, the note SHOULD contain the information necessary for a user to repeat the original request on the new URI. If the 307 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued. I'm using 302 for now, until I find THE correct answer.

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• PTLQueue : a scalable bounded-capacity MPMC queue

  - by Dave

  Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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• Dynamics CRM error "A currency is required if a value exists in a money field" after converting Acti

  - by Evgeny

  We have a Dynamics CRM 4.0 instance with some custom attributes of type "money" on the Case entity and on all Activity entities (Email, Phone Call, etc.) When I use the built-in "Convert Activity to Case" functionality I find that the resulting Case does not have a Currency set, even if the Activity it was created from does have it. Whenever the case is opened the user then gets this JavaScript error: A currency is required if a value exists in a money field. Select a currency and try again. This is extremely annoying! How do I fix it? Is there any way I can set the currency? It needs to be done synchronously, because the Case is opened immediately when it's created from an Activity. So even if I started a workflow to set the currency the user would still get that error at least once. Alterntatively, can I just suppress the warning somehow? I don't really care about setting the Currency, I just want the error gone. Thanks in advance for any help!

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• How to do custom display and auto-select in django admin multi-select field?

  - by rsp

  I'm new to django, so please feel free to tell me if I'm doing this incorrectly. I am trying to create a django ordering system. My order model: class Order(models.Model): ordered_by = models.ForeignKey(User, limit_choices_to = {'groups__name': "Managers", 'is_active': 1}) in my admin ANY user can enter an order, but ordered_by must be someone in the group "managers" (this is the behavior I want). Now, if the logged in user happens to be a manager I want it to automatically fill in the field with that logged in user. I have accomplished this by: class OrderAdmin(admin.ModelAdmin): def formfield_for_foreignkey(self, db_field, request, **kwargs): if db_field.name == "ordered_by": if request.user in User.objects.filter(groups__name='Managers', is_active=1): kwargs["initial"] = request.user.id kwargs["empty_label"] = "-------------" return db_field.formfield(**kwargs) return super(OrderAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs) This also works, but the admin puts the username as the display for the select box by default. It would be nice to have the user's real name listed. I was able to do it with this: class UserModelMultipleChoiceField(forms.ModelMultipleChoiceField): def label_from_instance(self, obj): return obj.first_name + " " + obj.last_name class OrderForm(forms.ModelForm): ordered_by = UserModelChoiceField(queryset=User.objects.all().filter(groups__name='Managers', is_active=1)) class OrderAdmin(admin.ModelAdmin): form = OrderForm My problem: I can't to both of these. If I put in the formfield_for_foreignkey function and add form = OrderForm to use my custom "UserModelChoiceField", it puts the nice name display but it won't select the currently logged in user. I'm new to this, but my guess is that when I use UserModelChoiceField it "erases" the info passed in via formfield_for_foreignkey. Do I need to use the super() function somehow to pass on this info? or something completely different?

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• SQL: How to select rows from a table while ignoring the duplicate field values?

  - by Maxxon

  How to select rows from a table while ignoring the duplicate field values? Here is an example: id user_id message 1 Adam "Adam is here." 2 Peter "Hi there this is Peter." 3 Peter "I am getting sick." 4 Josh "Oh, snap. I'm on a boat!" 5 Tom "This show is great." 6 Laura "Textmate rocks." What i want to achive is to select the recently active users from my db. Let's say i want to select the 5 recently active users. The problem is, that the following script selects Peter twice. mysql_query("SELECT * FROM messages ORDER BY id DESC LIMIT 5 "); What i want is to skip the row when it gets again to Peter, and select the next result, in our case Adam. So i don't want to show my visitors that the recently active users were Laura, Tom, Josh, Peter, and Peter again. That does not make any sense, instead i want to show them this way: Laura, Tom, Josh, Peter, (skipping Peter) and Adam. Is there an SQL command i can use for this problem?

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• Zend/PHP: Problem uploading/downloading file to/from MySQL's BLOB field.

  - by NAVEED

  I am uploading file(any type) like this: (It is uploading content of file in blob field of mysql) $organizationModel = new Model_Organization_Object( organizationId ); $myFile = file_get_contents( '../path/to/my/file/filename.ext' ); $organizationModel->setOrganizationProfile( $myFile ); $organizationModel->save(); Now I want to get that file from database and want to download. I doing this in controller's action: (I am aspecting pdf file here therefore it is hardcoded below. But in future I want to download any file from blob field) $organizationModel = new Model_Organization_Object( $organizationId ); $content = $organizationModel->getOrganizationProfile(); header('Content-Type: application/octet-stream'); header("Content-Length: " . strlen($content) ); header('Content-Disposition: attachment; filename=orgProfile.pdf'); $this->view->organizationProfile = $content; Now in view file I am doing this: echo $this-organizationProfile; But above download process print(echo) the content of file in firbug and does not download file in orignal format. My echo output in firebug is like this: %PDF-1.3 %???? 84 0 obj << /Linearized 1 /O 86 /H [ 541 212 ] /L 958398 /E 11238 /N 27 /T 956600 >> endobj xref 84 7 0000000016 00000 n 0000000486 00000 n 0000000753 00000 n 0000000982 00000 n 0000001102 00000 n 0000000541 00000 n 0000000732 00000 n trailer << /Size 91 /Info 83 0 R /Root 85 0 R /Prev 956590 /ID[<0a8d7035bf08791da591e8cae39b8c49><0a8d7035bf08791da591e8cae39b8c49>] >> startxref 0 %%EOF 85 0 obj << /Type /Catalog /Pages 82 0 R >> endobj 89 0 obj << /S 151 /Filter /FlateDecode /Length 90 0 R >> stream H?b```f``?e`b`?f`@\0?.????\\I~aV$?X??dO????bA?Az?lv1o#?{-????1+??G?????N`?b? >?-?? \0\0D40 endstream endobj 90 0 obj 106 endobj 86 0 obj << /Type /Page /Contents 87 0 R /Parent 79 0 R /Resources << /XObject << /img0 88 0 R >> /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ] >> /MediaBox [ 0 0 612 792 ] /CropBox [ 0 0 612 792 ] /Rotate 0 >> endobj 87 0 obj << /Filter /FlateDecode /Length 46 >> stream x?+T05???P0\0Bs#SC=S3c3??\\???t?|?@.\0??? endstream endobj 88 0 obj << /Filter /FlateDecode /Type /XObject /Length 8926 /BitsPerComponent 8 /Height 1122 /ColorSpace [ /Indexed /DeviceRGB 255 (\0\0\0JJJkkk{{{????????????????????????????????????\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\\ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0) ] /Subtype /Image /Width 793 >> stream x???v??\0?bF???mf?\\3??k?~? ?7uj??\\\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0~??/\0~??/\0~?&|??tp?pKS ????Fc???!?Q~?72?&???>???]?$?KUo????9?Tx??E8U}?????? _#=??6 Q{????v?T|s?>\\??w??.|??8?7Q????o.?o????????G??x??|?Is:??????oN>4???jJ?F?v? ? V?q<???P?????I>?.|?iT? ???Ç?Q?m????G?8c`????a`<?.|??~`????OG!?x7j??K*]??S?1??_??1\'?D?????0??\"?w\\?e?????<F:4????E-??Fa????O?v????9??_ m???P??8iuTr?i?FX?????<C? ????t:?(0??I>?2`????.???:??pv:???A??<$M??????e9??\\c???.0???t?kum?K;??<???\\@?]f/?h??m_???g???l?8&??*??2?-??Ew?4[j?v?(?????p?T???M--?8 cb??]?h??pN???kt?J$?m???X???5Cr?]?Jm?VP?X?Ð!? ?$???-?PM??O]??,?h???r=???qV}?p*?c?uq??t??????R6v??l8?I?e?9 {s\\K _?CN?^??W?8%p\']?2U?D{???Z?EB?*?d?va1^??Z\"?7?t]?TL?^??d???.|?4?q?2?&2??S{(??G?vNi4?D?K?)_^?]???D]DK???j?9????OQ?]???us?n?T4?om?P??E?|?t??w?????c?7>!]?\"}$??:??<????[9?C??Wi?u?su#9?\0?t?u=??=w??Q??A??.?dyb vN?N\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0??U/????<??v????S?A\\??qkm? !???&??J????!,??+?w;????{?!D???K×%5?E???????|n?FT*,? ?? ?j#Q??uT~r:}\\?_?????v???8Q?&? ???T?S?I\"?(>Y??????}H??aj?3??u?h?T?X?Z?-~??c\'P?^??d?????????]_???z??O]?q?????7??|?mN%??????T?????o???sUzT???m?v8?q? ??e]?wS???C~Ta???.??[%!??????2x]n~?7??????6.????K??;c }????r?)V?? u???*?7?$c\\???m?~???r??)U{?????????R?? ??D1L_????WUog?>??/?????????~?%???M???}\'?? ;???y??K`?????O?,??????<?,0???;3 #??m?v???aZ=?N?u?J`??dwnm;??.??k?n?K1-M?7????H&??????s?C??? ?}Z?1????c?(0?q?_1??7?%???G7U/??h9I??????S?Q??4nc?Lq??H6??;??c(/O??2???-?*_????%?I?/??I?o????ô?k??<????q??\'??]v?\"??+????,????qxgk?\\\\?6???7??Y???.G???Y??8??.??*???M_??J?hu1????z??W?o_??F?/???s?:?Y~??>0?g\\E?l?K5e???&L?/????k$????{?:\\>??Fs?-??l?>c??o?????9?V+?2;??}q?4 ?zS?|u?A`dK???n~?s???K?hiY?j??#p???S?M\\???0P2?\\*?m+?L5Er????[W?>9|???i?????}`Nmc:Qv??]&|?_????fx???????Ns~w??to????K?M???uN????0J6q1??u(b?M?_?????7?]?m?\':????S@???4?????\\??@~Mn?????|}?9?F6_Vr ??7??{?_??_????Y?Go?9??f1????E?|?Ucd? ????????t7k?? }??:??n?M?_????#?M$DG???:Z??y??;g:?|????F?m??e?F*?uJ?C??-?v?%??^?*??????z:l???w?e???9??i?5j???x?~??Ao???a?x?{?UL??? ??#:???\'^?????W??f;?u???ejq¯?u[?2K8??e?>/?ug?@S??L???? ??u0uI~?z?YYV???[[O?T??-Y?u?j?M?_???n&??7O?f??s??z`.`?,W??#?l??n???s??\'?????=??&#?z?M7_????s???x??y? ??u?p?G???0?e?G????8]{??N?1}??}~Q?[)?XF??_??*? p7iQ????M?(?l????????????f??6????*??U;@~\\k?i??w_??*?#???^?j?\\?L??/?}?Y?[??V??t~?w?n??a???m?O?(.?n;??ji:??W?ZnQ[9?n=?^??sE9??;?.??u3\"???<?L??y8?<H???g??u??\\?q???71p?U??}???f`?Y??m3b*C?t{?SX??7m<??6??8K??[Qs??&_??(M??:?Z???W?????W? ??4d??4?A????lw?e?d?>? ?pCV??h?SS?Z?T??4?N?,?? ?8=-?%???4?p?a??~??R?L??=J??j}??"??,?(?x?????????o?ï??t??X7???~jQ?aK???Z*YL????X??/?m?ot?9&s0???O5??j=?7sb?l?Mh???y?}Q\\4?MM?i5&?Yf??hS??N????\'?\0?????i?9??G?$??R?A1[??Y?t??4b?}????u??3?Y??Il????{??[u??f??q???Z_;??|*?t?uTO??}b?a?0>????>?>w\'P?E??]????6???v?^?,?;?uE?f?;?> yo?eNS@?C???I??????Otf????4I??? ?s????*??G?\'?>?</?=T?CE??5NR?~??%?1?d^V??O??????????e||/b??^ \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0~????+?W8??t????????}????????X?????7??/???\\}LM?????b?#?q];J??[U???(0N??t?????[??_V?!??%????-?7:?m???9??Dau?o]??^????*??,???h?o3f??[%?FW?W!?X#; ?>HC?-?\'/??^??\'?*?)??!?_?e?+TC?7O??I.?[?tN?,??Rs???u???^???????q??S??.?c?UR?????? ????M????FS???A????>?^K?|[?]z~7??7u???7V]L?|??l???]?[e?+u?????{U}???Em??IWbV7????/v?x?zk??F@.??5?G?Í>f??_???Gg?}??tc??&R???n???G-?N]/?w?? ????f?}Ue%?;?~?:????`6(??_???g???`? E~?p06?}#/?G=????;??<$Y???l??m?T??@Y??p?????r??.?H?>\0.Ih??~???!?N/^o? ??&v??R???9?suJ?r???JZg?z?Y?7??^?J??H>{[?vQ????qw?e{{?l????????u]?.Z?xh%7??>?|???b`?K?|I\"?nh?m?????m?z5Qpw??N3???y?)??k??????,?Ws*SJ]????????!?o?Iq3~x??Az{?v]\'?k????k???Dc ?]??l?)L??? I8eG#r?dC??;??/C???l???rm???????e?6?M??fP?4?r??)?!?\\s???{??!cN??h??>?? ??o>??m?dO=&<??P??]=]???n?v??y?l??\"?K??????rF?I???)Z??]n?J??N?w???S/S??w???R6}\'u??kN?K`?C/???N??,??o??I?>?S?(??hOV????-]?p?r??0??u?(?,a????/???\"o;???44????P?9K!O]??x?r?}??8?????w?4?|?el7U??l.}|w?- ?=?Lq??e<&??g?/z8??7??:n?????ï??~??_?a???&?7sy???,?3?1??rV???m?????s??C?x50?????g???\\??!??????e?????/Cl?Y???:??jz3??????/?a?]}??\\n???BZ?0?J-+u??????x?=??CC??M??W[??v<???S14?????\\C?Z ??g???q:?u?C?k?vc?K?;??\"Y?t?r]??G?z????w???r??????0??????e?:??/f?*^?W?Q8WsN??9}*?|??~x)?N?=6J?l????M?b??????M45?C?k]??r?u??????r ] Can someone help that how to download file or I am doing something wrong with uploading process. setOrganizationProfile() and getOrganizationProfile() function are created by me which are working fine while storing/getting data to/from database. Thanks

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• Sharepoint OLE DB - cannot insert records? "Field not updateable" error

  - by Pandincus

  I need to write a simple C# .NET application to retrieve, update, and insert some data in a Sharepoint list. I am NOT a Sharepoint developer, and I don't have control over our Sharepoint server. I would prefer not to have to develop this in a proper sharepoint development environment simply because I don't want to have to deploy my application on the Sharepoint server -- I'd rather just access data externally. Anyway, I found out that you can access Sharepoint data using OLE DB, and I tried it successfully using some ADO.NET: var db = DatabaseFactory.CreateDatabase(); DataSet ds = new DataSet(); using (var command = db.GetSqlStringCommand("SELECT * FROM List")) { db.LoadDataSet(command, ds, "List"); } The above works. However, when I try to insert: using (var command = db.GetSqlStringCommand("INSERT INTO List ([HeaderName], [Description], [Number]) VALUES ('Blah', 'Blah', 100)")) { db.ExecuteNonQuery(command); } I get this error: Cannot update 'HeaderName'; field not updateable. I did some Googling and apparently you cannot insert data through OLE DB! Does anyone know if there are some possible workarounds? I could try using Sharepoint Web Services, but I tried that initially and was having a heck of a time authenticating. Is that my only option?

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• Prototype or JQuery change the value of a hidden field?

  - by Nick Faraday

  I'm having some trouble with prototype changing the value of a hidden field. Function: function remove_fields (link) { $(link).next('input[type=hidden]').value = ''; $(link).up(".open_hours").hide(); } If I comment out the $(link).next('input[type=hidden]').value = ''; the hide function works. Trying to set the value gives me an error: $(link).next("input[type=hidden]") is undefined Here is my HTML around the function call: <div class="monday"> <div class ="open_hours"> <li><label for="location_monday">Monday</label> Open: 06:29PM - Close: 04:21PM <a href="#" onclick="remove_fields(this); return false;">remove</a></li> <li class="hidden optional" id="location_monday_open_input"><input id="location_monday_open" name="location[monday_open]" type="hidden" value="18:29:00" /></li> <li class="hidden optional" id="location_monday_close_input"><input class="close" id="location_monday_close" name="location[monday_close]" type="hidden" value="16:21:00" /></li> </div> </div> Not sure what I'm doing wrong here? Thanks Guys!

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• Flex HttpService POST limited to 543 Byte per Form field?

  - by motto

  Hi, I am getting a FaultEvent when trying to send form fields through HTTPService that contain more than 542 chars. Initializing the HttpService: httpServ = new HTTPService(); httpServ.method = 'POST'; httpServ.url = ENDPOINT_URL; //http://localhost:3001/ReportError.aspx httpServ.resultFormat = HTTPService.RESULT_FORMAT_TEXT; httpServ.contentType = HTTPService.CONTENT_TYPE_FORM; httpServ.addEventListener(ResultEvent.RESULT, OnErrorSent); httpServ.addEventListener(FaultEvent.FAULT, OnFault); Sending the request: var params:Object = {}; //params["stack"] = e.stackTrace.slice(0, 542); //length 542 = works //params["stack2"] = e.stackTrace.slice(1, 543); //length 542 = works (just to show that it's not about the content itself) params["stack3"] = e.stackTrace.slice(0, 543); //length 543 = fails I also seem to be able to create many form fields (with 542 length) so that it's not a limit of the request itself but of the form field: var params:Object = {}; params["stack"] = e.stackTrace.slice(0, 542); //length 542 params["stack2"] = e.stackTrace.slice(1, 543); //length 542 params["stack3"] = e.stackTrace.slice(2, 544); //length 542 // Length > 1600 chars The receiving party is an ASP.NET 4 site on the same domain and port. I hope someone already came across a similar restrictions or has some general advice on how to trace this problem down further. Thanks in advance.

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• Can you have a Dynamic Data Field which consists of a list of fields?

  - by Telos

  This is a purely theoretical question (at least until I start trying to implement it) but here goes. I wrote a web form a long time ago which has a configurable section for getting information. Basically for some customers there are no fields, for other customers there are up to 20 fields. I got it working by dynamically creating the fields at just the right time in the page lifecycle and going through a lot of headaches. 2 years later, I need to make some pretty big updates to this web form and there are some nifty new technologies. I've worked with ASP.NET Dynamic Data just a bit and, well, I half-crazed plan just occurred to me: The Ticket object has a one-to-many relationship to ExtendedField, we'll call that relationship Fields for brevity. Using that, the idea would be to create a FieldTemplate that dynamically generated the list of fields and displayed it. The big questions here would probably be: 1) Can a single field template resolve to multiple web controls without breaking things? 2) Can dynamic data handle updating/inserting multiple rows in such a fashion? 3) There was a third question I had a few minutes ago, but coworkers interrupted me and I forgot. So now the third question is: what is the third question? So basically, does this sound like it could work or am I missing a better/more obvious solution?

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• Asp MVC - "The Id field is required" validation message on Create; Id not set to [Required]

  - by burnt_hand

  This is happening when I try to create the entity using a Create style action in Asp.Net MVC 2. The POCO has the following properties: public int Id {get;set;} [Required] public string Message {get; set} On the creation of the entity, the Id is set automatically, so there is no need for it on the Create action. The ModelState says that "The Id field is required", but I haven't set that to be so. Is there something automatic going on here? EDIT - Reason Revealed The reason for the issue is answered by Brad Wilson via Paul Speranza in one of the comments below where he says (cheers Paul): You're providing a value for ID, you just didn't know you were. It's in the route data of the default route ("{controller}/{action}/{id}"), and its default value is the empty string, which isn't valid for an int. Use the [Bind] attribute on your action parameter to exclude ID. My default route was: new { controller = "Customer", action = "Edit", id = " " } // Parameter defaults EDIT - Update Model technique I actually changed the way I did this again by using TryUpdateModel and the exclude parameter array asscoiated with that. [HttpPost] public ActionResult Add(Venue collection) { Venue venue = new Venue(); if (TryUpdateModel(venue, null, null, new[] { "Id" })) { _service.Add(venue); return RedirectToAction("Index", "Manage"); } return View(collection); }

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• How can I get the rank of rows relative to total number of rows based on a field?

  - by Arms

  I have a scores table that has two fields: user_id score I'm fetching specific rows that match a list of user_id's. How can I determine a rank for each row relative to the total number of rows, based on score? The rows in the result set are not necessarily sequential (the scores will vary widely from one row to the next). I'm not sure if this matters, but user_id is a unique field. Edit @Greelmo I'm already ordering the rows. If I fetch 15 rows, I don't want the rank to be 1-15. I need it to be the position of that row compared against the entire table by the score property. So if I have 200 rows, one row's rank may be 3 and another may be 179 (these are arbitrary #'s for example only). Edit 2 I'm having some luck with this query, but I actually want to avoid ties SELECT s.score , s.created_at , u.name , u.location , u.icon_id , u.photo , (SELECT COUNT(*) + 1 FROM scores WHERE score > s.score) AS rank FROM scores s LEFT JOIN users u ON u.uID = s.user_id ORDER BY s.score DESC , s.created_at DESC LIMIT 15 If two or more rows have the same score, I want the latest one (or earliest - I don't care) to be ranked higher. I tried modifying the subquery with AND id > s.id but that ended up giving me an unexpected result set and different ties.

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• How to show a form field ONLY if another is selected in JavaScript or jQuery?

  - by Sam

  I have a form, like so: <form action="" method="post"> <select name="pageType"> <option value="main">Main Page</option> <option value="sub">Sub Page</option> <option value="sub-sub">Sub-Sub Page</option> </select> <br /> <label>Choose Sub Sub Name:</label> <input type="text" name="sub-sub-name" /> <br /> <input type="submit" name="submit" value="GO!" /> </form> What I would like to achive is for this text field (and it's label): <label>Choose Sub Sub Name:</label> <input type="text" name="sub-sub-name" /> to only appear if the 3rd option (sub sub page) is selected from the drop down and not show up otherwise. How can this be done with either javascript or the jquery framework? EDIT by the way, it would be nice if this can be achieved without the page needing to refresh and losing previously submitted form data. I know form data can still be kept using variables that store the values even on page refresh, but I was hoping for that effect that I see on a lot of sites where the additional text area (or other form element) just appears without page refresh.

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• Error: "an object reference is required for the non-static field, method or property..."

  - by user300484

  Hi! Im creating an application on C#. Its function is to evualuate if a given is prime and if the same swapped number is prime as well. When I build my solution on Visual Studio, it says that "an object reference is required for the non-static field, method or property...". Im having this problem with the "volteado" and "siprimo" methods. Can you tell me where is the problem and how i can fix it? thank you! namespace ConsoleApplication1 { class Program { static void Main(string[] args) { Console.Write("Write a number: "); long a= Convert.ToInt64(Console.ReadLine()); // a is the number given by the user long av = volteado(a); // av is "a" but swapped if (siprimo(a) == false && siprimo(av) == false) Console.WriteLine("Both original and swapped numbers are prime."); else Console.WriteLine("One of the numbers isnt prime."); Console.ReadLine(); } private bool siprimo(long a) {// evaluate if the received number is prime bool sp = true; for (long k = 2; k <= a / 2; k++) if (a % k == 0) sp = false; return sp; } private long volteado(long a) {// swap the received number long v = 0; while (a > 0) { v = 10 * v + a % 10; a /= 10; } return v; } } }

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• Asp MVC - "The Id field is required" validation message on Create; Id not set to [Required]

  - by Dann

  This is happening when I try to create the entity using a Create style action in Asp.Net MVC 2. The POCO has the following properties: public int Id {get;set;} [Required] public string Message {get; set} On the creation of the entity, the Id is set automatically, so there is no need for it on the Create action. The ModelState says that "The Id field is required", but I haven't set that to be so. Is there something automatic going on here? EDIT - Reason Revealed The reason for the issue is answered by Brad Wilson via Paul Speranza in one of the comments below where he says (cheers Paul): You're providing a value for ID, you just didn't know you were. It's in the route data of the default route ("{controller}/{action}/{id}"), and its default value is the empty string, which isn't valid for an int. Use the [Bind] attribute on your action parameter to exclude ID. My default route was: new { controller = "Customer", action = "Edit", id = " " } // Parameter defaults EDIT - Update Model technique I actually changed the way I did this again by using TryUpdateModel and the exclude parameter array asscoiated with that. [HttpPost] public ActionResult Add(Venue collection) { Venue venue = new Venue(); if (TryUpdateModel(venue, null, null, new[] { "Id" })) { _service.Add(venue); return RedirectToAction("Index", "Manage"); } return View(collection); }

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• Hibernate does not allow an embedded object with an int field to be null?

  - by Jason Novak

  Hibernate does not allow me to persist an object that contains an null embedded object with an integer field. For example, if I have a class called Thing that looks like this @Entity public class Thing { @Id public String id; public Part part; } where Part is an embeddable class that looks like this @Embeddable public class Part { public String a; public int b; } then trying to persist a Thing object with a null Part causes Hibernate to throw an Exception. In particular, this code Thing th = new Thing(); th.id = "thing.1"; th.part = null; session.saveOrUpdate(th); causes Hibernate to throw this Exception org.hibernate.PropertyValueException: not-null property references a null or transient value: com.ace.moab.api.jobs.Thing.part My guess is that this is happening because Part is an embedded class and so Part.a and Part.b are simply columns in the Thing database table. Since the Thing.part is null Hibernate wants to set the Part.a and Part.b column values to null for the row for thing.1. However, Part.b is an integer and Hibernate will not allow integer columns in the database to be null. This is what causes the Exception, right? So I am looking for workarounds for this problem. I noticed making Part.b an Integer instead of an int seems to work, but for reasons I won't bore you with this is not a good option for us. Thanks!

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• Symfony2 entity field type alternatives to "property" or "__toString()"?

  - by Polmonino

  Using Symfony2 entity field type one should specify property option: $builder->add('customers', 'entity', array( 'multiple' => true, 'class' => 'AcmeHelloBundle:Customer', 'property' => 'first', )); But sometimes this is not sufficient: think about two customers with the same name, so display the email (unique) would be mandatory. Another possibility is to implement __toString() into the model: class Customer { public $first, $last, $email; public function __toString() { return sprintf('%s %s (%s)', $this->first, $this->last, $this->email); } } The disadvances of the latter is that you are forced to display the entity the same way in all your forms. Is there any other way to make this more flexible? I mean something like a callback function: $builder->add('customers', 'entity', array( 'multiple' => true, 'class' => 'AcmeHelloBundle:Customer', 'property' => function($data) { return sprintf('%s %s (%s)', $data->first, $data->last, $data->email); }, ));

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• What is the best / proper idiom in django for modifying a field during a .save() where you need to o

  - by MDBGuy

  Hi, say I've got: class LogModel(models.Model): message = models.CharField(max_length=512) class Assignment(models.Model): someperson = models.ForeignKey(SomeOtherModel) def save(self, *args, **kwargs): super(Assignment, self).save() old_person = #????? LogModel(message="%s is no longer assigned to %s"%(old_person, self).save() LogModel(message="%s is now assigned to %s"%(self.someperson, self).save() My goal is to save to LogModel some messages about who Assignment was assigned to. Notice that I need to know the old, presave value of this field. I have seen code that suggests, before super().save(), retrieve the instance from the database via primary key and grab the old value from there. This could work, but is a bit messy. In addition, I plan to eventually split this code out of the .save() method via signals - namely pre_save() and post_save(). Trying to use the above logic (Retrieve from the db in pre_save, make the log entry in post_save) seemingly fails here, as pre_save and post_save are two seperate methods. Perhaps in pre_save I can retrieve the old value and stick it on the model as an attribute? I was wondering if there was a common idiom for this. Thanks.

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• In ArrayBlockingQueue, why copy into ReentrantLock field into local final variable?

  - by mjlee

  In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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• Do the 'up to date' guarantees provided by final field in Java's memory model extend to indirect ref

  - by mattbh

  The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?

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• How to obtain value of auto_increment field in Access linked to MySQL?

  - by Cruachan

  I'm trying to modify and existing Access application to use MySQL as a database via ODBC with the minimal amount of recoding. The current code will often insert a new record using DAO then obtain the ID by using LastModified. This doesn't work with MySQL. Instead I'm trying to use the approach using SELECT * FROM tbl_name WHERE auto_col IS NULL Suggested for Access in the MySQL documentation. However if I set up a sample table consisting of just an id and text data field and execute this CurrentDb.Execute ("INSERT INTO tbl_scratch (DATA) VALUES ('X')") Set rst = CurrentDb.OpenRecordset("SELECT id FROM tbl_scratch WHERE id IS NULL") myid = rst!id Id is returned as null. However if I execute INSERT INTO tbl_scratch (DATA) VALUES ('X'); SELECT id FROM tbl_scratch WHERE id IS NULL; using a direct MySQL editor then id is returned correctly, so my database and approach is fine but my implementation inside Access must be incorrect. Frustratingly the MySQL documentation gives the SQL statement to retrieve the id as an example that works in Access (as it states LAST_INSERT_ID() doesn't) but gives no further details. How might I fix this?

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• In ArrayBlockingQueue, why copy final member field into local final variable?

  - by mjlee

  In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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• How to focus next field if user clicked on the link?

  - by LA_

  I have a number of fields with labels-links like below: <div class="control-group"> <label class="control-label" for="some-id-1"><a href="http://example.com/some-id-1" target="_blank">Text1</a></label> <div class="controls"> <input type="text" id="some-id-1" name="some-id-1"><br> </div> </div> <div class="control-group"> <label class="control-label" for="some-id-2"><a href="http://example.com/some-id-2" target="_blank">Text2</a></label> <div class="controls"> <input type="text" id="some-id-2" name="some-id-2"><br> </div> </div> If user clicks on the link, how can I focus according field (without preventing default action)? I.e. if user clicks on Text1, then I should open http://example.com/some-id-1 in new window and set focus at input with id some-id-1.

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