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Thread safe method in c#

    Question

  • Hi All,

     

    I search in google about thread safe method in c#, but there are several methods to do so.

     

    Is there any best method to be thread safe and easy to implement?

     

    Thanks.

    Sunday, August 26, 2007 3:38 PM

Answers

  • Hello Alexander_HK,

     

    Thread safe will very much depend on its intended usage. Some types naturally end up being used only within a single thread, others naturally end up being shared across threads, and some are used specifically for thread handling, and often have their own special characteristics.Based on my understanding to thread safe methods, you can try to refer to the following thread safe models:

    1.Thread-safe static methods, unsafe instance methods:

     This is the most commonly found model in the framework. Basically, any static methods can be called by any thread at any time with no nasty side-effects.Instance methods, however, should only be called on a single thread at a time, and there should really be a memory barrier (in the calling code) before using an instance that has previous been used by another thread, and another memory barrier (again, in the calling code) after changing an instance that is thereafter going to be used by another thread.

     

    2.Methods and properties using thread-local storage:

     Some methods and properties naturally use thread-local storage - that is to say, each thread has its own individual value for a variable. Thread.CurrentPrincipal is a good example of this - compare it with Thread.CurrentCulture, which is an instance property. Most methods and properties using thread-local storage are static, just like Thread.CurrentPrincipal - having one value per instance and per thread rarely makes sense, and indeed the simplest way of using thread-local storage is with ThreadStaticAttribute which can only be applied to static fields (which can then be returned by static properties, etc).

     

    3.Totally thread-safe types:

    Sometimes, it's important for a type to be totally thread-safe, so that anyone can use any instance of it from any thread, with no internal inconsistencies or unwanted side-effects. This is particularly true of types which are typically accessed using the factory or singleton pattern. Encoding is a good example of this - it would be a pain if threads couldn't use Encoding.ASCII (or any other encoding) without carefully locking things.

     

    Often, types like this are immutable - once they've been created, they don't change, so even without locking, it doesn't matter what you do with them. Assuming instances are acquired in a thread-safe way to start with (which usually involves a lock or a type initializer to ensure safety), immutable types are naturally thread-safe.

     

    4.Types with limited thread safety:

    Some types can be accessed in some ways by multiple threads, but not in others. Many collections fall into this category. For instance, from the documentation for ArrayList:

    An ArrayList can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

    So, you can populate an instance in one thread, and thereafter read the contents from multiple threads. The documentation doesn't specify anything about handing over an instance from one thread to another (such as whether the client code has to make sure there's a memory barrier after the last write and another before the first read in another thread), which is unfortunate, but probably means you can't rely on it. This kind of case is where clear documentation is absolutely crucial. If a type can support multiple threads doing one thing and another thread doing something else (multiple reader, single writer tending to be the most common form) then the documentation should state exactly what is entailed - is that level of safety available without any extra locking on the part of the client, what are the guarantees about how soon that any "new" data is seen by other threads, etc.

     

    You can try to check out this article for more details - http://www.yoda.arachsys.com/csharp/threads/threadsafe.shtml

    Here is an article about “A Short Guide to Mastering Thread-Safety" for your reference - http://www.thinkingparallel.com/2006/10/15/a-short-guide-to-mastering-thread-safety/

     

    Here are some examples using delegate to keep thread safety for your reference.

    1).Control.Invoke Method - http://msdn2.microsoft.com/en-us/library/zyzhdc6b.aspx

    2).Control.BeginInvoke Method - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.begininvoke.aspx

    3).control.creategraphics - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.creategraphics.aspx

     

    Hope this helps,

     

    Citizens on the earth

     

    Tuesday, August 28, 2007 3:47 AM
  •  Citizen on the earth wrote:

    Hello Alexander_HK,

     

    Thread safe will very much depend on its intended usage. Some types naturally end up being used only within a single thread, others naturally end up being shared across threads, and some are used specifically for thread handling, and often have their own special characteristics.Based on my understanding to thread safe methods, you can try to refer to the following thread safe models:

    1.Thread-safe static methods, unsafe instance methods:

     This is the most commonly found model in the framework. Basically, any static methods can be called by any thread at any time with no nasty side-effects.Instance methods, however, should only be called on a single thread at a time, and there should really be a memory barrier (in the calling code) before using an instance that has previous been used by another thread, and another memory barrier (again, in the calling code) after changing an instance that is thereafter going to be used by another thread.

     

    2.Methods and properties using thread-local storage:

     Some methods and properties naturally use thread-local storage - that is to say, each thread has its own individual value for a variable. Thread.CurrentPrincipal is a good example of this - compare it with Thread.CurrentCulture, which is an instance property. Most methods and properties using thread-local storage are static, just like Thread.CurrentPrincipal - having one value per instance and per thread rarely makes sense, and indeed the simplest way of using thread-local storage is with ThreadStaticAttribute which can only be applied to static fields (which can then be returned by static properties, etc).

     

    3.Totally thread-safe types:

    Sometimes, it's important for a type to be totally thread-safe, so that anyone can use any instance of it from any thread, with no internal inconsistencies or unwanted side-effects. This is particularly true of types which are typically accessed using the factory or singleton pattern. Encoding is a good example of this - it would be a pain if threads couldn't use Encoding.ASCII (or any other encoding) without carefully locking things.

     

    Often, types like this are immutable - once they've been created, they don't change, so even without locking, it doesn't matter what you do with them. Assuming instances are acquired in a thread-safe way to start with (which usually involves a lock or a type initializer to ensure safety), immutable types are naturally thread-safe.

     

    4.Types with limited thread safety:

    Some types can be accessed in some ways by multiple threads, but not in others. Many collections fall into this category. For instance, from the documentation for ArrayList:

    An ArrayList can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

    So, you can populate an instance in one thread, and thereafter read the contents from multiple threads. The documentation doesn't specify anything about handing over an instance from one thread to another (such as whether the client code has to make sure there's a memory barrier after the last write and another before the first read in another thread), which is unfortunate, but probably means you can't rely on it. This kind of case is where clear documentation is absolutely crucial. If a type can support multiple threads doing one thing and another thread doing something else (multiple reader, single writer tending to be the most common form) then the documentation should state exactly what is entailed - is that level of safety available without any extra locking on the part of the client, what are the guarantees about how soon that any "new" data is seen by other threads, etc.

     

    You can try to check out this article for more details - http://www.yoda.arachsys.com/csharp/threads/threadsafe.shtml

    Here is an article about “A Short Guide to Mastering Thread-Safety" for your reference - http://www.thinkingparallel.com/2006/10/15/a-short-guide-to-mastering-thread-safety/

     

    Here are some examples using delegate to keep thread safety for your reference.

    1).Control.Invoke Method - http://msdn2.microsoft.com/en-us/library/zyzhdc6b.aspx

    2).Control.BeginInvoke Method - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.begininvoke.aspx

    3).control.creategraphics - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.creategraphics.aspx

     

    Hope this helps,

     

    Citizens on the earth

     

    A class (static) method is not thread-safe by default, no more thread safe than an instance method.  An instance method that modifies instance data is not thread-safe (but it doesn't have to modify instance data).  A class method can modify class data and render it not thread-safe.  Any method (class or instance) that modifies shared data is not thread safe.  You must synchronize access to that shared data to make it thread safe.
    Tuesday, August 28, 2007 1:42 PM
    Moderator

All replies

  • It is a windows apaplication, not a console one

    Sunday, August 26, 2007 3:41 PM
  • Hello Alexander_HK,

     

    Thread safe will very much depend on its intended usage. Some types naturally end up being used only within a single thread, others naturally end up being shared across threads, and some are used specifically for thread handling, and often have their own special characteristics.Based on my understanding to thread safe methods, you can try to refer to the following thread safe models:

    1.Thread-safe static methods, unsafe instance methods:

     This is the most commonly found model in the framework. Basically, any static methods can be called by any thread at any time with no nasty side-effects.Instance methods, however, should only be called on a single thread at a time, and there should really be a memory barrier (in the calling code) before using an instance that has previous been used by another thread, and another memory barrier (again, in the calling code) after changing an instance that is thereafter going to be used by another thread.

     

    2.Methods and properties using thread-local storage:

     Some methods and properties naturally use thread-local storage - that is to say, each thread has its own individual value for a variable. Thread.CurrentPrincipal is a good example of this - compare it with Thread.CurrentCulture, which is an instance property. Most methods and properties using thread-local storage are static, just like Thread.CurrentPrincipal - having one value per instance and per thread rarely makes sense, and indeed the simplest way of using thread-local storage is with ThreadStaticAttribute which can only be applied to static fields (which can then be returned by static properties, etc).

     

    3.Totally thread-safe types:

    Sometimes, it's important for a type to be totally thread-safe, so that anyone can use any instance of it from any thread, with no internal inconsistencies or unwanted side-effects. This is particularly true of types which are typically accessed using the factory or singleton pattern. Encoding is a good example of this - it would be a pain if threads couldn't use Encoding.ASCII (or any other encoding) without carefully locking things.

     

    Often, types like this are immutable - once they've been created, they don't change, so even without locking, it doesn't matter what you do with them. Assuming instances are acquired in a thread-safe way to start with (which usually involves a lock or a type initializer to ensure safety), immutable types are naturally thread-safe.

     

    4.Types with limited thread safety:

    Some types can be accessed in some ways by multiple threads, but not in others. Many collections fall into this category. For instance, from the documentation for ArrayList:

    An ArrayList can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

    So, you can populate an instance in one thread, and thereafter read the contents from multiple threads. The documentation doesn't specify anything about handing over an instance from one thread to another (such as whether the client code has to make sure there's a memory barrier after the last write and another before the first read in another thread), which is unfortunate, but probably means you can't rely on it. This kind of case is where clear documentation is absolutely crucial. If a type can support multiple threads doing one thing and another thread doing something else (multiple reader, single writer tending to be the most common form) then the documentation should state exactly what is entailed - is that level of safety available without any extra locking on the part of the client, what are the guarantees about how soon that any "new" data is seen by other threads, etc.

     

    You can try to check out this article for more details - http://www.yoda.arachsys.com/csharp/threads/threadsafe.shtml

    Here is an article about “A Short Guide to Mastering Thread-Safety" for your reference - http://www.thinkingparallel.com/2006/10/15/a-short-guide-to-mastering-thread-safety/

     

    Here are some examples using delegate to keep thread safety for your reference.

    1).Control.Invoke Method - http://msdn2.microsoft.com/en-us/library/zyzhdc6b.aspx

    2).Control.BeginInvoke Method - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.begininvoke.aspx

    3).control.creategraphics - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.creategraphics.aspx

     

    Hope this helps,

     

    Citizens on the earth

     

    Tuesday, August 28, 2007 3:47 AM
  •  Citizen on the earth wrote:

    Hello Alexander_HK,

     

    Thread safe will very much depend on its intended usage. Some types naturally end up being used only within a single thread, others naturally end up being shared across threads, and some are used specifically for thread handling, and often have their own special characteristics.Based on my understanding to thread safe methods, you can try to refer to the following thread safe models:

    1.Thread-safe static methods, unsafe instance methods:

     This is the most commonly found model in the framework. Basically, any static methods can be called by any thread at any time with no nasty side-effects.Instance methods, however, should only be called on a single thread at a time, and there should really be a memory barrier (in the calling code) before using an instance that has previous been used by another thread, and another memory barrier (again, in the calling code) after changing an instance that is thereafter going to be used by another thread.

     

    2.Methods and properties using thread-local storage:

     Some methods and properties naturally use thread-local storage - that is to say, each thread has its own individual value for a variable. Thread.CurrentPrincipal is a good example of this - compare it with Thread.CurrentCulture, which is an instance property. Most methods and properties using thread-local storage are static, just like Thread.CurrentPrincipal - having one value per instance and per thread rarely makes sense, and indeed the simplest way of using thread-local storage is with ThreadStaticAttribute which can only be applied to static fields (which can then be returned by static properties, etc).

     

    3.Totally thread-safe types:

    Sometimes, it's important for a type to be totally thread-safe, so that anyone can use any instance of it from any thread, with no internal inconsistencies or unwanted side-effects. This is particularly true of types which are typically accessed using the factory or singleton pattern. Encoding is a good example of this - it would be a pain if threads couldn't use Encoding.ASCII (or any other encoding) without carefully locking things.

     

    Often, types like this are immutable - once they've been created, they don't change, so even without locking, it doesn't matter what you do with them. Assuming instances are acquired in a thread-safe way to start with (which usually involves a lock or a type initializer to ensure safety), immutable types are naturally thread-safe.

     

    4.Types with limited thread safety:

    Some types can be accessed in some ways by multiple threads, but not in others. Many collections fall into this category. For instance, from the documentation for ArrayList:

    An ArrayList can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

    So, you can populate an instance in one thread, and thereafter read the contents from multiple threads. The documentation doesn't specify anything about handing over an instance from one thread to another (such as whether the client code has to make sure there's a memory barrier after the last write and another before the first read in another thread), which is unfortunate, but probably means you can't rely on it. This kind of case is where clear documentation is absolutely crucial. If a type can support multiple threads doing one thing and another thread doing something else (multiple reader, single writer tending to be the most common form) then the documentation should state exactly what is entailed - is that level of safety available without any extra locking on the part of the client, what are the guarantees about how soon that any "new" data is seen by other threads, etc.

     

    You can try to check out this article for more details - http://www.yoda.arachsys.com/csharp/threads/threadsafe.shtml

    Here is an article about “A Short Guide to Mastering Thread-Safety" for your reference - http://www.thinkingparallel.com/2006/10/15/a-short-guide-to-mastering-thread-safety/

     

    Here are some examples using delegate to keep thread safety for your reference.

    1).Control.Invoke Method - http://msdn2.microsoft.com/en-us/library/zyzhdc6b.aspx

    2).Control.BeginInvoke Method - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.begininvoke.aspx

    3).control.creategraphics - http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.creategraphics.aspx

     

    Hope this helps,

     

    Citizens on the earth

     

    A class (static) method is not thread-safe by default, no more thread safe than an instance method.  An instance method that modifies instance data is not thread-safe (but it doesn't have to modify instance data).  A class method can modify class data and render it not thread-safe.  Any method (class or instance) that modifies shared data is not thread safe.  You must synchronize access to that shared data to make it thread safe.
    Tuesday, August 28, 2007 1:42 PM
    Moderator