StaticCriticalSection source code

[TheVinn]

Here is a StaticCriticalSection object. It functions as a static/global CriticalSection, but one that is guaranteed to be in a correct initialized state before any code runs, including constructors for other objects with static storage duration (i.e. global class objects). Usage example at the bottom:

REMOVED AND REPLACED BY A MORE GENERIC CLASS THAT WORKS FOR ANY OBJECT

Here:
viewtopic.php?f=6&t=6995

[zamrate]

Could you maybe give an example when using a normal CriticalSection as static variable would not work? I've done that quite a lot in my code, but never have had any problems (until now!).

[TheVinn]

Could you maybe give an example when using a normal CriticalSection as static variable would not work? I've done that quite a lot in my code, but never have had any problems (until now!).

Two cases:

1) CriticalSection at function scope with static storage duration. Example:

Code: Select all

void calledFromMultipleThreads ()
{
  static CriticalSection mutex;
  // Race condition causes double initializion with some build environments
  CriticalSection::ScopedLockType lock (mutex);
}


2) CriticalSection at file scope with static storage duration, accessed from a constructor of an object at file scope with static storage duration. Example:

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//foo.cpp
CriticalSection globalMutex;

//bar.cpp
extern CriticalSection globalMutex;
struct Singleton {
  Singleton ()
  {
    CriticalSection::ScopedLockType lock (globalMutex);
    // Will fail if we execute before globalLock constructor
  }
};
Singleton globalSingleton; // Will fail depending on order of constructors


StaticCriticalSection solves both cases. In c++0x condition #1 is fixed (but #2 is still a problem).

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namespace { struct PrivateTag { }; } // distinguishes the StaticCriticalSection
void safelyCalledFromMultipleThreads ()
{
  StaticCriticalSection <PrivateTag> mutex;
  StaticCriticalSection <PrivateTag>::ScopedLockType lock (mutex);
  // Works correctly when called from multiple threads
}


and

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//common.h
struct GlobalMutexTag { };

//foo.cpp
StaticCriticalSection <GlobalMutexTag> globalMutex;

//bar.cpp
extern StaticCriticalSection <GlobalMutexTag> globalMutex;
struct Singleton
{
  Singleton ()
  {
    StaticCriticalSection <GlobalMutexTag>::ScopedLockType lock (globalMutex);
    // Works no matter what the order of construction
  }
};
Singleton globalSingleton; // Always constructs properly no matter what the order


[TheVinn]

never have had any problems (until now!).

Did you really discover a problem or do you think you have an issue only because of what I exposed regarding function level statics?

[zamrate]

No, I never had any problems at all with static CriticalSection so far. But it's nice to know that there could be some potential problems.