View source for DevHelp OpenEventSem

{{DISPLAYTITLE:DevHelp_OpenEventSem}}
This service opens a 32-bit shared event semaphore. 

==Syntax==
===C===
<PRE>
USHORT APIENTRY DevHelp_OpenEventSem(ULONG hEvent );
</PRE>

===Assembler===
<PRE>
MOV   EAX,SemaphoreHandle     ; DWORD semaphore handle
MOV   DL,DevHlp_OpenEventSem

CALL  [Device_Help]
</PRE>
==Parameters==
===C===
; hEvent (ULONG): Semaphore handle

===Assembler===
<PRE>
MOV   EAX,SemaphoreHandle     ; DWORD semaphore handle
MOV   DL,DevHlp_OpenEventSem

CALL  [Device_Help]
</PRE>

==Return Code==

===C===
     Success Indicator: 0
 
            Possible errors:
               ERROR_INVALID_HANDLE       (6)
               ERROR_NOT_ENOUGH_MEMORY    (8)
               ERROR_TOO_MANY_OPENS       (291)

===Assembler===
<PRE>
   'C' Clear if successful.

   'C' Set if error.
       EAX = Error code.
            Possible errors:
               ERROR_INVALID_HANDLE         (6)
               ERROR_NOT_ENOUGH_MEMORY      (8)
               ERROR_TOO_MANY_OPENS         (291)
</PRE>

==Remarks==
This function uses the EAX and FLAGS registers. OpenEventSem can be called only from a Ring 0 physical 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, then ERROR_INVALID_HANDLE is returned.

The OPEN/CLOSE operations can be nested. A maximum of 65,534 (64KB-1) opens-per-process are allowed for each semaphore at any one time. If this limit is reached, the 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===
<PRE>
#include  "dhcalls.h"

USHORT APIENTRY DevHelp_OpenEventSem(ULONG hEvent );
</PRE>

==Related Functions==

[[Category:DevHlps]]