DevHelp CloseEventSem

This service closes an event semaphore that was previously opened with OpenEventSem. If this is the last reference to this event, then the event semaphore is destroyed.

Syntax

C

USHORT APIENTRY DevHelp_CloseEventSem( ULONG hEvent );

Assembler

MOV   EAX,SemaphoreHandle              ; DWORD semaphore handle
MOV   DL,DevHlp_CloseEventSem

CALL  [Device_Help]

Parameters

C

hEvent (ULONG) -input

Semaphore handle

Assembler

MOV   EAX,SemaphoreHandle              ; DWORD semaphore handle
MOV   DL,DevHlp_CloseEventSem

CALL  [Device_Help]

Return Code

C

Success Indicator: Clear if successful.

Possible errors: ERROR_INVALID_HANDLE (6)

Assembler

   'C' Clear if successful.

   'C' Set if error.
       EAX = Error code.
            Possible errors:
               ERROR_INVALID_HANDLE (6)

Remarks

This function uses the EAX and Flags registers. CloseEventSem can be called only from a Ring 0 device driver or file system driver. The handle passed in must be a handle to a shared event semaphore. If the handle does not exist or is not a shared event semaphore, or if the semaphore was not previously opened with OpenEventSem, then ERROR_INVALID_HANDLE is returned.

The system semaphores reside in a memory buffer rather than on a disk file. Therefore, when the last process that has a semaphore open exits or closes that semaphore, the semaphore disappears.

The OPEN/CLOSE operations can be nested. A maximum of 65,534 (64KB-1) opens-per-process is allowed for each semaphore at any one time. If this limit is reached, the very next call to OpenEventSem returns ERROR_TOO_MANY_OPENS. In order for a process to intentionally destroy a semaphore prior to termination, the number of calls to CloseEventSem must equal the number of calls to OpenEventSem.

Example Code

C

#include  "dhcalls.h"

USHORT APIENTRY DevHelp_CloseEventSem( ULONG hEvent );