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OK to copy a CRITICAL_SECTION?

Answer 1

+5 A:

No. A CRITICAL_SECTION cannot be copied. MSDN states this explicitly:

A critical section object cannot be moved or copied.

James McNellis 2010-07-16 22:27:26

Answer 2

+1 A:

A quick search through the headers reveals that the structure is defined in winnt.h, and this definition clearly seems to indicate that copying the structure wouldn't work.

typedef struct _RTL_CRITICAL_SECTION {
    PRTL_CRITICAL_SECTION_DEBUG DebugInfo;

    //
    //  The following three fields control entering and exiting the critical
    //  section for the resource
    //

    LONG LockCount;
    LONG RecursionCount;
    HANDLE OwningThread;        // from the thread's ClientId->UniqueThread
    HANDLE LockSemaphore;
    ULONG_PTR SpinCount;        // force size on 64-bit systems when packed
} RTL_CRITICAL_SECTION, *PRTL_CRITICAL_SECTION;

That said, I have no idea why these internal counters are stored in a user-space structure, i.e. what will happen if a program modifies these?

casablanca 2010-07-16 22:36:47

The documentation clearly states that you cannot modify the contents of a `CRITICAL_SECTION`: "The process must also not modify the object, but must treat it as logically opaque."

James McNellis 2010-07-16 22:39:50

Which is why I raised this question. What does "cannot" mean? It's uncommon for anything beyond a handle to be manipulable by user programs.

casablanca 2010-07-16 23:31:02

@casablanca: If an API says that a consumer of the API _must_ not do something, that means "if you do this, all bets are off."

James McNellis 2010-07-16 23:48:55

And a critical section is intended to be *FAST*. That means that it can't spend the time entering the kernel and leaving to enter. If you want a synchronization object that provides similar semantics to a critical section, use a mutex object. Then you don't have to worry about all those internal details being exposed ot the application. Of course your application will be a lot slower than the critical section but that's the price you pay for architectural purity.

Larry Osterman 2010-07-17 02:12:34

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OK to copy a CRITICAL_SECTION?

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