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• Do really need a count lock on Multi threads with one CPU core?

  - by MrROY

  If i have some code looks like this(Please ignore the syntax, i want to understand it without a specified language): count = 0 def countDown(): count += 1 if __name__ == '__main__': thread1(countDown) thread2(countDown) thread3(countDown) Here i have a CPU with only one core, do i really need a lock to the variable count in case of it could be over-written by other threads. I don't know, but if the language cares a lot, please explain it under Java?C and Python, So many thanks.

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• Using locks inside a loop

  - by Xaqron

  // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Do I need to syncronize thread access to an int

  - by Martin Harris

  I've just written a method that is called by multiple threads simultaneously and I need to keep track of when all the threads have completed, the code uses this pattern: private void RunReport() { _reportsRunning++; try { //code to run the report } finally { _reportsRunning--; } } This is the only place within the code that _reportsRunning's value is changed, and the method takes about a second to run. Occasionally when I have more than six or so threads running reports together the final result for _reportsRunning can get down to -1, if I wrap the calls to _runningReports++ and _runningReports-- in a lock then the behaviour appears to be correct and consistant. So, to the question: When I was learning multithreading in C++ I was taught that you didn't need to synchronize calls to increment and decrement operations because they were always one assembly instruction and therefore it was impossible for the thread to be switched out mid-call. Was I taught correctly, and if so how come that doesn't hold true for C#?

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• how can we achieve second application read that file when first application not modifying it

  - by soField

  i have two application first application is bash second is java which one of them is periodically deleting and recreating a specific file (first) the other one is also periodically reading this file and process it in it's own logic (second) how can we achieve second application read that file when first application not modifying it my aim is to force second app read the file only when content of file fully written inside it how can achieve this goal ?

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• Multi-threading concept and lock in c#

  - by Neeraj

  I read about lock, though not understood nothing at all. My question is why do we use a un-used object and lock that and how this makes something thread-safe or how this helps in multi-threading ? Isn't there other way to make thread-safe code. public class test { private object Lock { get; set; } ... lock (this.Lock) { ... } ... } Sorry is my question is very stupid, but i don't understand, although i've used it many times.

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• Can I lock rows in a cursor if the cursor only returns a single count(*) row?

  - by RenderIn

  I would like to restrict users from inserting more than 3 records with color = 'Red' in my FOO table. My intentions are to A) retrieve the current count so that I can determine whether another record is allowed and B) prevent any other processes from inserting any Red records while this one is in process, hence the for update of. I'd like to do something like: cursor cur_cnt is select count(*) cnt from foo where foo.color = 'Red' for update of foo.id; Will this satisfy both my requirements or will it not lock only the rows in the count(*) who had foo.color = 'Red'?

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• Thread-Safe lazy instantiating using MEF

  - by Xaqron

  // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Will calling a File.Exist put a lock on a file?

  - by yaya7

  Hi, If I am trying to delete a file, but at the same time another process is performing a File.Exists(...) on the same file, will that potentially lock the file and cause my process to fail?

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• detection of 'flush tables with read lock' in php

  - by theduke0

  I would like to know from my application if a myisam table can accept writes (i.e. not locked). If an exception is thrown, everything is fine as I can catch this and log the failed statement to a file. However, if a 'flush tables with read lock' command has been issued (possibly for backup), the query I send will pretty much hang out forever. If one table is locked at a time, insert delayed works well. But when this global lock is applied, my query just waits. The query I run is an insert statement. If this statement fails or hangs, user experience is degraded. I need a way to send the query to the server and forget about it (pretty much). Does anyone have any suggestions on how to deal with this? -set a query timeout? -run asyncronous request and allow for the lock to expire while application continues? -fork my php process? Please let me know if I can provide and clarification or details.

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• Lock innoDB table temporarily

  - by Industrial

  Hi everyone, I make bigger inserts consisting of a couple of thousand rows in my current web app and I would like to make sure that no one can do anything but read the table, until the inserts have been done. What is the best way to do this while keeping the read availability open for normal, non-admin users? Thanks!

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• What is better and why to use List as thread safe: BlockingCollection or ReaderWriterLockSlim or lock?

  - by theateist

  I have System.Collections.Generic.List _myList and many threads can read from it or add items to it simultaneously. From what I've read I should using 'BlockingCollection' so this will work. I also read about ReaderWriterLockSlim' and 'lock', but I don't figure out how to use them instead ofBlockingCollection`, so my question is can I do the same with: ReaderWriterLockSlim lock instead of using 'BlockingCollection'. If YES, can you please provide simple example and what pros and cons of using BlockingCollection, ReaderWriterLockSlim, lock?

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• Best practice for avoiding locks on a heavily read table?

  - by Luiggi

  Hi, I have a big database (~4GB), with 2 large tables (~3M records) having ~180K SELECTs/hour, ~2k UPDATEs/hour and ~1k INSERTs+DELETEs/hour. What would be the best practice to guarantee no locks for the reading tasks while inserting/updating/deleting? I was thinking about using a NOLOCK hint, but there is so much discussed about this (is good, is bad, it depends) that I'm a bit lost. I must say I've tried this in a dev environment and I didn't find any problems, but I don't want to put it on production until I get some feedback... Thank you! Luiggi

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• VB.NET Program Locks Up with Internet Explorer Opened

  - by aaronsj

  I'm using Visual Studio 2008 and developing a VB.NET application. I'm having strange lockup problems with my program, but only when Internet explorer 8 is opened. When I cover my form with another window and then uncover it, I find that it has locked up. My program has no references to IE and the only thing it even has to do with IE is using Process.Start with a web address. My program works fine and exactly as it should, but only when IE is not opened. Does anyone know why a program would lock up only while IE is running? Edit: I've done some digging and I've found the offending thread in my program. I don't know what starts this thread or what it does, but when I kill it, my program no longer freezes. The thread is one of the CreateApplicationContext threads, here is the last few items in the stack trace of that thread. 6 ntkrnlpa.exe+0x897bc 7 ntdll.dll!KiFastSystemCallRet 8 mscorwrks.dll!LogHelp_TerminateOnAssert+0x61 9 mscorwrks.dll!DllUnregisterServerInternal+0x10523 10 mscorwrks.dll!DllUnregisterServerInternal+0x10542 11 mscorwrks.dll!StrongNameErrorInfo+0x34387 12 mscorwrks.dll!StrongNameErrorInfo+0x34815 13 mscorwrks.dll!CreateApplicationContext+0xbc35 14 KERNEL32.dll!GetModuleHandleA+0xdf Process explorer says my program is using no CPU nor throwing any exceptions while it is hung.

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• ActiveRecord and transactionsin between `before_save` and `save`

  - by JP

  I have some logic in before_save whereby (only) when some conditions are met I let the new row be created with special_number equal to the maximum special_number in the database + 1. (If the conditions aren't met then I do something different, so I can't use auto-increments) My worry is that two threads acting on this database at once might pick the same special_number if the second is executed while the first is saving. Is there way to lock the database between before_save and finishing the save, but only in some cases? I know all saves are sent in transactions, will this do the job for me? def before_save if things_are_just_right # -- Issue some kind of lock? # -- self.lock? I have no idea # Pick new special_number new_special = self.class.maximum('special_number') + 1 write_attribute('special_number',new_special) else # No need to lock in this case write_attribute('special_number',some_other_number) end end

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• How to lock a transaction for reading a row and then inserting in Hibernate?

  - by at

  I have a table with a name and a name_count. So when I insert a new record, I first check what the maximum name_count is for that name. I then insert the record with that maximum + 1. Works great... except with mysql 5.1 and hibernate 3.5, by default the reads don't respect transaction boundaries. 2 of these inserts for the same name could happen at the same time and end up with the same name_count, which completely screws my application! Unfortunately, there are some specific situations where the above is actually fairly common. So what do I do? I assume I can do a pessimistic lock where any row I read is locked for further reading until I commit or roll-back my transaction. Or I can do an optimistic lock with a version column that automatically keeps trying until there are no conflicts? What's the best approach for my situation and how do I specify it in Hibernate 3.5 and mysql 5.1? The above table is massive and accessed frequently.

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• What happens if you break out of a Lock() statement?

  - by cyclotis04

  I'm writing a program which listens to an incoming TcpClient and handles data when it arrives. The Listen() method is run on a separate thread within the component, so it needs to be threadsafe. If I break out of a do while loop while I'm within a lock() statement, will the lock be released? If not, how do I accomplish this? Thanks! (Any other advice on the subject of Asynchronous TCP Sockets is welcome as well.) private void Listen() { do { lock (_client) { if (!_client.Connected) break; lock (_stateLock) { if (!_listening) break; if (_client.GetStream().DataAvailable) HandleData(); } } Thread.Sleep(0); } while (true); }

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• Real World Examples of read-write in concurrent software

  - by Richard Fabian

  I'm looking for real world examples of needing read and write access to the same value in concurrent systems. In my opinion, many semaphores or locks are present because there's no known alternative (to the implementer,) but do you know of any patterns where mutexes seem to be a requirement? In a way I'm asking for candidates for the standard set of HARD problems for concurrent software in the real world.

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• How can I modify the application file of an application that is currently running (on Linux)?

  - by Hach-Que

  I have an application running called AppFS. This application has an ext2 filesystem just attached to the end of the file (it's positioned so that the application binary exists in a 1MB spacing area, followed by the ext2 data). Now I've got FUSE embedded in the program and I've managed to extract the filesystem out of the application data into a temporary file so that FUSE can mount / use it. The problem I have now is writing the temporary file back into the application file. I get "Text file busy" presumably because the application has locked itself and won't let writes occur. Is there a way I can force the file to become unlocked so I can write data to it? (It's important to note that I'm not changing the application binary area - just rewriting the ext2 component.) It needs to be unlocked without requiring root permissions (unlocked by the same user who started the application).

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• Copy a value based on criteria Salesforce

  - by Robert

  Hi all, On a Salesforce.com opportunity I have a number of custom fields that are potential options that the end client will eventually select. Option 1 (Desc Field) Option 1 (Value) Option 2 (Desc Field) Option 2 (Value) Option 3 (Desc Field) Option 3 (Value) At a future point the user will ultimately choose one of the options as the preferred option. What I want is then the value for the chosen option to be stored in another field without the user having to enter it again. A “nice to have” would also be that all 3 option descriptions, values and selected value are locked once this is done. Any ideas?

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• How to create "lock" (stop updating of cells) in Excel?

  - by Oozi

  My question is pretty simple, but one to which I can't really find a solution myself. I use Excel quite frequently, but rarely the fancy stuff. Anyway, to the point: How do I create a dropmenu that will lock certain cells, rows or columns? (by lock I mean unable to change via hand and stops updating itself). Example: A1 = 5 B1 = A1 * 100 Can I "lock" the B1-cell, so that changing A1 will have no effect on B1 (Will remain at value 500)? I would preferably want to be able to "unlock" the cell as well, instead of simply making function into value. Is this possible? Thanks in advance!

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• What are the differences between various threading synchronization options in C#?

  - by user38834

  Can someone explain the difference between: lock (someobject) {} Using Mutex Using Semaphore Using Monitor Using Other .Net synchronization classes I just can't figure it out. It seems to me the first two are the same?

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• ASP.NET Page.Cache versus Page.Application storage for data synchronization?

  - by jdk

  Both Page.Cache and Page.Application can store an application's "global" data, shared among requests and threads. How should one storage area be chosen over the other considering scenarios of data synchronization in the multi-threaded ASP.NET environment? Looking for best practice and experienced recommendation.

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• Does multiple files in SQL Server when using RAID help reduce conflicts in growth and file-locking?

  - by Dr Giles M

  I've been reading around and get the impression that if you are using RAID then using multiple SQL Server files within a filegroup won't yeild any more improvements, and the benefits are purely administrative (if you started to run out of space or wanted to partition off data into managable chunks for backups/balancing the data around your big server room). However, being a reasonably savvy software person, it's not unthinkable to hypothesise that, even for smaller databases that SQL Server will perform growth and locking operations (for writes) on a LOGICAL file basis, so even if you are using RAID, it seems to make sense to have multiple files in a file group to balance I/O, or does the time taken to reconstruct the data from distributed filegroups outweigh the benefits of reduced locking? I'm also aware that the behaviour and benefits may be different for tables/indeces/log. Is there a good site that distinguishes the benefits of multiple files when RAID is already in place?

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• How to prevent screen locking when lid is closed?

  - by Joe Casadonte

  I have Ubuntu 11.10 with Gnome 3 (no Unity), gnome-screen-saver has been removed and replaced with xscreensaver. The screensaver stuff all works fine -- no complaints there. When I close my laptop lid, even for a second, the screen locks (and the dialog box asking for my password is xscreensaver's). I'd like for this not to happen... Things I've tried/looked at already: xscreensaver settings - the "Lock Screen After" checkbox is not checked (though I've also tried it checked and set to 720 minutes) gconf-editor - apps -> gnome-screensaver -> lock_enabled is not checked System Settings - Power - "When the lid is closed" is set to "Do nothing" for both battery and A/C System Settings - Screen - Lock is "off" gconf-editor - apps -> gnome-power-manager -> buttons -> lid_ac && lid_battery are both set to "nothing" dconf-editor - apps -> org -> gnome -> desktop -> screensaver -> lock_enabled is not checked Output from: gsettings list-recursively org.gnome.settings-daemon.plugins.power: org.gnome.settings-daemon.plugins.power active true org.gnome.settings-daemon.plugins.power button-hibernate 'hibernate' org.gnome.settings-daemon.plugins.power button-power 'suspend' org.gnome.settings-daemon.plugins.power button-sleep 'suspend' org.gnome.settings-daemon.plugins.power button-suspend 'suspend' org.gnome.settings-daemon.plugins.power critical-battery-action 'hibernate' org.gnome.settings-daemon.plugins.power idle-brightness 30 org.gnome.settings-daemon.plugins.power idle-dim-ac false org.gnome.settings-daemon.plugins.power idle-dim-battery true org.gnome.settings-daemon.plugins.power idle-dim-time 10 org.gnome.settings-daemon.plugins.power lid-close-ac-action 'nothing' org.gnome.settings-daemon.plugins.power lid-close-battery-action 'nothing' org.gnome.settings-daemon.plugins.power notify-perhaps-recall true org.gnome.settings-daemon.plugins.power percentage-action 2 org.gnome.settings-daemon.plugins.power percentage-critical 3 org.gnome.settings-daemon.plugins.power percentage-low 10 org.gnome.settings-daemon.plugins.power priority 1 org.gnome.settings-daemon.plugins.power sleep-display-ac 600 org.gnome.settings-daemon.plugins.power sleep-display-battery 600 org.gnome.settings-daemon.plugins.power sleep-inactive-ac false org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 0 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'suspend' org.gnome.settings-daemon.plugins.power sleep-inactive-battery true org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout 0 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type 'suspend' org.gnome.settings-daemon.plugins.power time-action 120 org.gnome.settings-daemon.plugins.power time-critical 300 org.gnome.settings-daemon.plugins.power time-low 1200 org.gnome.settings-daemon.plugins.power use-time-for-policy true gnome-settings-daemon is running: <~> $ ps -ef | grep gnome-settings-daemon 1000 1719 1645 0 19:37 ? 00:00:01 /usr/lib/gnome-settings-daemon/gnome-settings-daemon 1000 1726 1 0 19:37 ? 00:00:00 /usr/lib/gnome-settings-daemon/gsd-printer 1000 1774 1645 0 19:37 ? 00:00:00 /usr/lib/gnome-settings-daemon/gnome-fallback-mount-helper Anything else I can check? Thanks!

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• How can I view locking on a file on a file?

  - by JamesP

  Hi all, We have a database file (foxpro) on a Windows share (2003 server), we're having some problems where the program that writes to this file has to retry as the file is locked, this all happens very quickly and within a few seconds the file is available but the problem is it shouldn't be locked. Does anyone know how we can view what's locking it? Any tools available? Thanks James

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