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Are All the Static/Shared Methods in .NET Thread Safe?I was often noted by Thread Safety declarations when I was reading .NET Framework Class Library documents in MSDN.
The declaration is usually described as 'Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.' So, does this mean All the static/shared methods written in .NET compatible programming language, such as C#, VB.NET, are guaranteed to be synchronized and thread safe? Or else, we still need to implement our custom code to ensure the thread-safty for static methods? > The declaration is usually described as 'Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members arenot guaranteed to be thread safe.' So, does this mean All the static/shared methods written in .NET compatible programming language, such as C#, VB.NET, are guaranteed to be synchronized and thread safe? Yes. I have never heard of a static (Shared) method *not* being thread-safe. The reason that static / Shared methods are always thread-safe is because there is no instance of a class, and therefore, no member variables for threads to stomp on in contradictory ways. Any local variables inside a static / Shared method exist locally within the particular stack frame of the calling code on the calling thread, and therefore, will never conflict with multiple threads simultaneously hitting the same method with local variables. -- Peace & happy computing, Mike Labosh, MCSD MCT Owner, vbSensei.Com "Escriba coda ergo sum." -- vbSensei Not necessarily true. If the static/shared method contains internal state
variables that it maintains across calls, it may not be thread safe if the implementer didn't ensure internal thread safety. That said, I don't believe there are any non-thread safe static/shared methods in the framework itself, but given the size of the framework, I don't think you can guarantee that any given method is thread safe without referring to the documentation. Mike Ober. Show quote "Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote in message news:eDOOpAvaHHA.4520@TK2MSFTNGP06.phx.gbl... >> The declaration is usually described as 'Any public static (Shared in > Visual Basic) members of this type are thread safe. Any instance members > are > not guaranteed to be thread safe.' > So, does this mean All the static/shared methods written in .NET > compatible > programming language, such as C#, VB.NET, are guaranteed to be > synchronized > and thread safe? > > Yes. I have never heard of a static (Shared) method *not* being > thread-safe. > > The reason that static / Shared methods are always thread-safe is because > there is no instance of a class, and therefore, no member variables for > threads to stomp on in contradictory ways. > > Any local variables inside a static / Shared method exist locally within > the > particular stack frame of the calling code on the calling thread, and > therefore, will never conflict with multiple threads simultaneously > hitting > the same method with local variables. > -- > > Peace & happy computing, > > Mike Labosh, MCSD MCT > Owner, vbSensei.Com > > "Escriba coda ergo sum." -- vbSensei > > Show quote
"Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote in message Not necessarily true. See Array.Resize for instance, which needs a class news:eDOOpAvaHHA.4520@TK2MSFTNGP06.phx.gbl... >> The declaration is usually described as 'Any public static (Shared in > Visual Basic) members of this type are thread safe. Any instance members > are > not guaranteed to be thread safe.' > So, does this mean All the static/shared methods written in .NET > compatible > programming language, such as C#, VB.NET, are guaranteed to be > synchronized > and thread safe? > > Yes. I have never heard of a static (Shared) method *not* being > thread-safe. > > The reason that static / Shared methods are always thread-safe is because > there is no instance of a class, and therefore, no member variables for instance. > threads to stomp on in contradictory ways. And what about static member variables?> > Any local variables inside a static / Shared method exist locally within > the > particular stack frame of the calling code on the calling thread, and > therefore, will never conflict with multiple threads simultaneously > hitting > the same method with local variables. Show quote > -- > > Peace & happy computing, > > Mike Labosh, MCSD MCT > Owner, vbSensei.Com > > "Escriba coda ergo sum." -- vbSensei > > On Mar 20, 8:03 am, "Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote: But there could be static fields. Those would have to be synchronized> The reason that static / Shared methods are always thread-safe is because > there is no instance of a class, and therefore, no member variables for > threads to stomp on in contradictory ways. > just like instance fields. The reason why Microsoft chose to make most static properties and methods thread-safe is because they're commonly used across many threads and it would incovenient for the callers to figure out how to synchronize them on their own. Imagine what it would look like if Console.WriteLine had to be wrapped with a lock everytime. That's just plain nasty. On Mar 20, 1:03 pm, "Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote: And what about static variables?> The reason that static / Shared methods are always thread-safe is because > there is no instance of a class, and therefore, no member variables for > threads to stomp on in contradictory ways. > Any local variables inside a static / Shared method exist locally within the With reference types, two different threads could still be accessing> particular stack frame of the calling code on the calling thread, and > therefore, will never conflict with multiple threads simultaneously hitting > the same method with local variables. the same *objects*, even though the local variables themselves are independent. Basically, whenever there's shared data, there can be threading issues. There's nothing to stop static methods sharing data with other executing code, therefore there can be threading issues. Jon Any method (static or otherwise) that is called by multiple threads and uses
any shared state must be aware of syncronization and take require action depending on needs. Static != thread safe. -- William Stacey [C# MVP] Show quote "Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote in message news:eDOOpAvaHHA.4520@TK2MSFTNGP06.phx.gbl... |> The declaration is usually described as 'Any public static (Shared in | Visual Basic) members of this type are thread safe. Any instance members are | not guaranteed to be thread safe.' | So, does this mean All the static/shared methods written in .NET compatible | programming language, such as C#, VB.NET, are guaranteed to be synchronized | and thread safe? | | Yes. I have never heard of a static (Shared) method *not* being | thread-safe. | | The reason that static / Shared methods are always thread-safe is because | there is no instance of a class, and therefore, no member variables for | threads to stomp on in contradictory ways. | | Any local variables inside a static / Shared method exist locally within the | particular stack frame of the calling code on the calling thread, and | therefore, will never conflict with multiple threads simultaneously hitting | the same method with local variables. | -- | | Peace & happy computing, | | Mike Labosh, MCSD MCT | Owner, vbSensei.Com | | "Escriba coda ergo sum." -- vbSensei | | Thanks!
Show quote "William Stacey [C# MVP]" <william.sta***@gmail.com> wrote in message news:OpVKL5vaHHA.3272@TK2MSFTNGP03.phx.gbl... > Any method (static or otherwise) that is called by multiple threads and > uses > any shared state must be aware of syncronization and take require action > depending on needs. Static != thread safe. > > -- > William Stacey [C# MVP] > > > "Mike Labosh" <mlabosh_at_hotmail_dot_com> wrote in message > news:eDOOpAvaHHA.4520@TK2MSFTNGP06.phx.gbl... > |> The declaration is usually described as 'Any public static (Shared in > | Visual Basic) members of this type are thread safe. Any instance members > are > | not guaranteed to be thread safe.' > | So, does this mean All the static/shared methods written in .NET > compatible > | programming language, such as C#, VB.NET, are guaranteed to be > synchronized > | and thread safe? > | > | Yes. I have never heard of a static (Shared) method *not* being > | thread-safe. > | > | The reason that static / Shared methods are always thread-safe is > because > | there is no instance of a class, and therefore, no member variables for > | threads to stomp on in contradictory ways. > | > | Any local variables inside a static / Shared method exist locally within > the > | particular stack frame of the calling code on the calling thread, and > | therefore, will never conflict with multiple threads simultaneously > hitting > | the same method with local variables. > | -- > | > | Peace & happy computing, > | > | Mike Labosh, MCSD MCT > | Owner, vbSensei.Com > | > | "Escriba coda ergo sum." -- vbSensei > | > | > > "Laser Lu" <laser***@163.com> schrieb: No.>The declaration is usually described as 'Any >public static (Shared in Visual Basic) members >of this type are thread safe. Any instance >members are not guaranteed to be thread safe.' >So, does this mean All the static/shared >methods written in .NET compatible programming >language, such as C#, VB.NET, are guaranteed >to be synchronized and thread safe? -- M S Herfried K. Wagner M V P <URL:http://dotnet.mvps.org/> V B <URL:http://dotnet.mvps.org/dotnet/faqs/> A-ha, quite agree with u. The most brief and definite answer.:)
Show quote "Cor Ligthert [MVP]" <notmyfirstn***@planet.nl> wrote in message news:eW%23ay73aHHA.4872@TK2MSFTNGP03.phx.gbl... > In my idea to the best answer > > Here's the deal... the only difference (that I am aware of) between
static and instance methods is that instance methods pass the "this" pointer silently while static methods do not; that's it. I think that the reason why static methods have been marked as "thread safe" is that they are assuming that, since the method is static, you won't be accessing any shared-state as you most likely would in an instance method. Both instance methods and static methods *are* thread-safe as long as you don't access any shared-state (eg. instance/static fields) since each thread has its own local stack. In short, if you have a multi-threaded application that needs to access shared-state, you need to synchronize all access via a locking mechanism such as lock, mutexes, monitor, etc... Here's a link that might help : http://www.odetocode.com/Articles/313.aspx Regards, Anthony Show quote On Mar 20, 4:08 am, "Laser Lu" <laser***@163.com> wrote: > I was often noted by Thread Safety declarations when I was reading .NET Framework Class Library documents in MSDN. > The declaration is usually described as 'Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.' > So, does this mean All the static/shared methods written in .NET compatible programming language, such as C#, VB.NET, are guaranteed to be synchronized and thread safe? Or else, we still need to implement our custom code to ensure the thread-safty for static methods? Thanks for your reply. Now, I've had a better understanding based on your
explaination.:) Show quote "Anthony Paul" <anthonypa***@gmail.com> wrote in message news:1174411917.631303.248680@e65g2000hsc.googlegroups.com... > Here's the deal... the only difference (that I am aware of) between > static and instance methods is that instance methods pass the "this" > pointer silently while static methods do not; that's it. I think that > the reason why static methods have been marked as "thread safe" is > that they are assuming that, since the method is static, you won't be > accessing any shared-state as you most likely would in an instance > method. Both instance methods and static methods *are* thread-safe as > long as you don't access any shared-state (eg. instance/static fields) > since each thread has its own local stack. > > In short, if you have a multi-threaded application that needs to > access shared-state, you need to synchronize all access via a locking > mechanism such as lock, mutexes, monitor, etc... > > Here's a link that might help : http://www.odetocode.com/Articles/313.aspx > > Regards, > > Anthony > > On Mar 20, 4:08 am, "Laser Lu" <laser***@163.com> wrote: >> I was often noted by Thread Safety declarations when I was reading .NET >> Framework Class Library documents in MSDN. >> The declaration is usually described as 'Any public static (Shared in >> Visual Basic) members of this type are thread safe. Any instance members >> are not guaranteed to be thread safe.' >> So, does this mean All the static/shared methods written in .NET >> compatible programming language, such as C#, VB.NET, are guaranteed to be >> synchronized and thread safe? Or else, we still need to implement our >> custom code to ensure the thread-safty for static methods? > > They are marked thread-safe, only when the *author (in this case MS) has
taken the time to verify they are thread safe (which is easy if they don't touch shared data). As most statics in the framework (not sure if all are) are documented with the thread safe attribute, it is easy to assume that is some kind of special gaureentee all statics give - which is not the case. You can easily make a non thread safe static method via bug or on purpose. -- William Stacey [C# MVP] Show quote "Anthony Paul" <anthonypa***@gmail.com> wrote in message Framework Class Library documents in MSDN.news:1174411917.631303.248680@e65g2000hsc.googlegroups.com... | Here's the deal... the only difference (that I am aware of) between | static and instance methods is that instance methods pass the "this" | pointer silently while static methods do not; that's it. I think that | the reason why static methods have been marked as "thread safe" is | that they are assuming that, since the method is static, you won't be | accessing any shared-state as you most likely would in an instance | method. Both instance methods and static methods *are* thread-safe as | long as you don't access any shared-state (eg. instance/static fields) | since each thread has its own local stack. | | In short, if you have a multi-threaded application that needs to | access shared-state, you need to synchronize all access via a locking | mechanism such as lock, mutexes, monitor, etc... | | Here's a link that might help : http://www.odetocode.com/Articles/313.aspx | | Regards, | | Anthony | | On Mar 20, 4:08 am, "Laser Lu" <laser***@163.com> wrote: | > I was often noted by Thread Safety declarations when I was reading .NET | > The declaration is usually described as 'Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.' | > So, does this mean All the static/shared methods written in .NET compatible programming language, such as C#, VB.NET, are guaranteed to be synchronized and thread safe? Or else, we still need to implement our custom code to ensure the thread-safty for static methods? Show quote | |  |
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