 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
.NET Forum / .NET Framework / CLR / July 2004When to use Synchronized method and When to use lock?
To prevent concurrent access to a data structure, one way is to use its Synchronized method, another way is to use unlock keyword in C#. I'd like to know how to choose from them. For example : class MyClass { ArrayList list = new ArrayList(); void Method(object newObj) { // One way : ArrayList l = ArrayList.Synchronized(list); .... // Another way : lock(this) { ... } } } What's the difference between this two methods? Thanks! > To prevent concurrent access to a data structure, one way is to use its > Synchronized method, another way is to use unlock keyword in C#. I'd like to [quoted text clipped - 16 lines] > > What's the difference between this two methods? Thanks! I would personally recommend locking, but not on "this". Using the synchronized wrappers only makes each operation synchronized - you still have to lock (on the SyncRoot) for any sequence of operations you want to be atomic (such as iterating through the list). See http://www.pobox.com/~skeet/csharp/multithreading.html#lock.choice for more about choosing what to lock on.  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet If replying to the group, please do not mail me too Thanks! > > To prevent concurrent access to a data structure, one way is to use its > > Synchronized method, another way is to use unlock keyword in C#. I'd like to [quoted text clipped - 25 lines] > http://www.pobox.com/~skeet/csharp/multithreading.html#lock.choice for > more about choosing what to lock on. >To prevent concurrent access to a data structure, one way is to use its >Synchronized method, another way is to use unlock keyword in C#. I'd like to >know how to choose from them. Easy. Don't use Synchronized, ever. Always use lock (list.SyncRoot). Signaturehttp://www.kynosarges.de Thanks. But why? > >To prevent concurrent access to a data structure, one way is to use its > >Synchronized method, another way is to use unlock keyword in C#. I'd like to > >know how to choose from them. > > Easy. Don't use Synchronized, ever. Always use lock (list.SyncRoot). >Thanks. But why? Because Synchronized only gives the illusion of thread safety. For example, the following code is NOT thread-safe: ArrayList list = new ArrayList(); ArrayList syncList = ArrayList.Synchronized(list); ... int index = syncList.IndexOf(foo); if (index >= 0) syncList[index] = bar; Between calling IndexOf and changing the object at index, another thread might jump in and change the contents of syncList. This is possible because Synchronized protects only individual operations, not sequences of two or more operations. By contrast, the following code IS thread-safe (provided all other threads also call lock (list.SyncRoot) before accessing the list): lock (list.SyncRoot) { int index = list.IndexOf(foo); if (index >= 0) list[index] = bar; } Signaturehttp://www.kynosarges.de Thanks. I see . > >Thanks. But why? > [quoted text clipped - 19 lines] > if (index >= 0) list[index] = bar; > }
Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.