Waits for ownership of the specified critical section object. The function returns when the calling thread is granted ownership.

Syntax

void WINAPI EnterCriticalSection(
  __inout  LPCRITICAL_SECTION lpCriticalSection
);

Parameters

lpCriticalSection [in, out]

A pointer to the critical section object.

Return Value

This function does not return a value.

This function can raise EXCEPTION_POSSIBLE_DEADLOCK if a wait operation on the critical section times out. The timeout interval is specified by the following registry value: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\CriticalSectionTimeout. Do not handle a possible deadlock exception; instead, debug the application.

Windows 2000:  In low memory situations, EnterCriticalSection can raise an exception. Do not attempt to handle this exception; instead, either terminate the process or allow the exception to pass to the unhandled exception filter. To avoid an exception due to low memory, call the InitializeCriticalSectionAndSpinCount function to preallocate the event used by EnterCriticalSection instead of calling the InitializeCriticalSection function, which forces EnterCriticalSection to allocate the event. Preallocating the event is not necessary on Windows XP or later because EnterCriticalSection is guaranteed not to fail due to lack of resources.

Remarks

The threads of a single process can use a critical section object for mutual-exclusion synchronization. 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 InitializeCriticalSection or InitializeCriticalSectionAndSpinCount to initialize the object.

To enable mutually exclusive access to a shared resource, each thread calls the EnterCriticalSection or TryEnterCriticalSection function to request ownership of the critical section before executing any section of code that accesses the protected resource. The difference is that TryEnterCriticalSection returns immediately, regardless of whether it obtained ownership of the critical section, while EnterCriticalSection blocks until the thread can take ownership of the critical section. When it has finished executing the protected code, the thread uses the LeaveCriticalSection function to relinquish ownership, enabling another thread to become owner and access the protected resource. There is no guarantee about the order in which waiting threads will acquire ownership of the critical section.

After a thread has ownership of a critical section, it can make additional calls to EnterCriticalSection or TryEnterCriticalSection without blocking its execution. This prevents a thread from deadlocking itself while waiting for a critical section that it already owns. The thread enters the critical section each time EnterCriticalSection and TryEnterCriticalSection succeed. A thread must call LeaveCriticalSection once for each time that it entered the critical section.

Any thread of the process can use the DeleteCriticalSection function to release the system resources that were allocated when the critical section object was initialized. After this function has been called, the critical section object can no longer be used for synchronization.

If a thread terminates while it has ownership of a critical section, the state of the critical section is undefined.

If a critical section is deleted while it is still owned, the state of the threads waiting for ownership of the deleted critical section is undefined.

Examples

For an example that uses EnterCriticalSection, see Using Critical Section Objects.

Requirements

See Also

Critical Section Objects

DeleteCriticalSection

InitializeCriticalSection

InitializeCriticalSectionAndSpinCount

LeaveCriticalSection

Synchronization Functions

TryEnterCriticalSection

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Build date: 7/2/2009