GlobalUnlock function (winbase.h)

Article
10/13/2021

Decrements the lock count associated with a memory object that was allocated with GMEM_MOVEABLE. This function has no effect on memory objects allocated with GMEM_FIXED.

Note The global functions have greater overhead and provide fewer features than other memory management functions. New applications should use the heap functions unless documentation states that a global function should be used. For more information, see Global and Local Functions.

Syntax

BOOL GlobalUnlock(
  [in] HGLOBAL hMem
);

Parameters

[in] hMem

A handle to the global memory object. This handle is returned by either the GlobalAlloc or GlobalReAlloc function.

Return value

If the memory object is still locked after decrementing the lock count, the return value is a nonzero value. If the memory object is unlocked after decrementing the lock count, the function returns zero and GetLastError returns NO_ERROR.

If the function fails, the return value is zero and GetLastError returns a value other than NO_ERROR.

Remarks

The internal data structures for each memory object include a lock count that is initially zero. For movable memory objects, the GlobalLock function increments the count by one, and GlobalUnlock decrements the count by one. For each call that a process makes to GlobalLock for an object, it must eventually call GlobalUnlock. Locked memory will not be moved or discarded, unless the memory object is reallocated by using the GlobalReAlloc function. The memory block of a locked memory object remains locked until its lock count is decremented to zero, at which time it can be moved or discarded.

Memory objects allocated with GMEM_FIXED always have a lock count of zero. If the specified memory block is fixed memory, this function returns TRUE.

If the memory object is already unlocked, GlobalUnlock returns FALSE and GetLastError reports ERROR_NOT_LOCKED.

A process should not rely on the return value to determine the number of times it must subsequently call GlobalUnlock for a memory object.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Target Platform	Windows
Header	winbase.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll