| Platform SDK: DLLs, Processes, and Threads |
The InitializeCriticalSectionAndSpinCount function initializes a critical section object and sets the spin count for the critical section.
BOOL InitializeCriticalSectionAndSpinCount( LPCRITICAL_SECTION lpCriticalSection, // critical section DWORD dwSpinCount // spin count );
If the high-order bit is set, the function preallocates the event used by the EnterCriticalSection function. Do not set this bit if you are creating a large number of critical section objects, because it will consume a significant amount of nonpaged pool.
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError.
In low memory situations, InitializeCriticalSectionAndSpinCount can raise a STATUS_NO_MEMORY exception.
The threads of a single process can use a critical section object for mutual-exclusion synchronization. There is no guarantee about the order in which threads will obtain ownership of the critical section, however, the system will be fair to all threads.
The process is responsible for allocating the memory used by a critical section object, which it can do by declaring a variable of type CRITICAL_SECTION. Before using a critical section, some thread of the process must call the InitializeCriticalSection or InitializeCriticalSectionAndSpinCount function to initialize the object. You can subsequently modify the spin count by calling the SetCriticalSectionSpinCount function.
After a critical section object has been initialized, the threads of the process can specify the object in the EnterCriticalSection, TryEnterCriticalSection, or LeaveCriticalSection function to provide mutually exclusive access to a shared resource. For similar synchronization between the threads of different processes, use a mutex object.
A critical section object cannot be moved or copied. The process must also not modify the object, but must treat it as logically opaque. Use only the critical section functions provided by the Win32 API to manage critical section objects.
The spin count is useful for critical sections of short duration that can experience high levels of contention. Consider a worst-case scenario, in which an application on an SMP system has two or three threads constantly allocating and releasing memory from the heap. The application serializes the heap with a critical section. In the worst-case scenario, contention for the critical section is constant, and each thread makes an expensive call to the WaitForSingleObject function. However, if the spin count is set properly, the calling thread will not immediately call WaitForSingleObject when contention occurs. Instead, the calling thread can acquire ownership of the critical section if it is released during the spin operation.
You can improve performance significantly by choosing a small spin count for a critical section of short duration. The heap manager uses a spin count of roughly 4000 for its per-heap critical sections. This gives great performance and scalability in almost all worst-case scenarios.
Windows NT/2000: Requires Windows NT 4.0 SP3 or later.
Windows 95/98: Requires Windows 98.
Header: Declared in Winbase.h; include Windows.h.
Library: Use Kernel32.lib.
Synchronization Overview, Synchronization Functions, InitializeCriticalSection, SetCriticalSectionSpinCount, WaitForSingleObject