WinWaitEventSem: Difference between revisions
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WinWaitEventSem blocks until the specified event semaphore is posted. Event semaphores are edge-triggered. This means that if the semaphore is posted and reset before a waiting thread has a chance to run, the waiting thread will still act as though the semaphore is posted. | |||
=== Syntax === | === Syntax === | ||
WinWaitEventSem( ''hevSemaphore'', ''ulTimeOut'' ) | |||
=== Parameters === | === Parameters === | ||
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|Error, The caller was blocked for ''ulTimeout'' milliseconds but ownership of the semaphore could not be obtained within this time limit, Time has expired. | |Error, The caller was blocked for ''ulTimeout'' milliseconds but ownership of the semaphore could not be obtained within this time limit, Time has expired. | ||
|} | |} | ||
=== Gotchas === | === Gotchas === | ||
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=== Sample Code === | === Sample Code === | ||
<pre> | <pre> | ||
#define INCL_WINMESSAGEMGR | #define INCL_WINMESSAGEMGR | ||
#include | #include <os2.h> | ||
HEV hevMySemaphore; /* MySemaphore handle */ | HEV hevMySemaphore; /* MySemaphore handle */ | ||
Revision as of 05:34, 8 December 2017
WinWaitEventSem blocks until the specified event semaphore is posted. Event semaphores are edge-triggered. This means that if the semaphore is posted and reset before a waiting thread has a chance to run, the waiting thread will still act as though the semaphore is posted.
Syntax
WinWaitEventSem( hevSemaphore, ulTimeOut )
Parameters
- HEV hevSemaphore (input)
- The handle of the semaphore to be released.
- ULONG ulTimeout (input)
- The number of milliseconds the function will wait before returning.
- Set to SEM_IMMEDIATE_RETURN (0), the function will return immediately regardless of whether or not the semaphore is posted.
- Set to SEM_INDEFINITE_WAIT (-1), the function will block indefinitely (forever) until the semaphore is posted.
Returns
APIRET rc
The following values can be returned:
| 0 | NO_ERROR | Successfully obtained semaphore ownership |
| 6 | ERROR_INVALID_HANDLE | Error, The value in phevSemaphore does not point to a valid semaphore, The calling process must first have access to the semaphore in question |
| 8 | ERROR_NOT_ENOUGH_MEMORY | Error, The system memory limit has been exhausted |
| 95 | ERROR_INTERRUPT | Error, The thread has become unblocked by an external event such as an exception, ownership
has not been obtained |
| 640 | ERROR_TIMEOUT | Error, The caller was blocked for ulTimeout milliseconds but ownership of the semaphore could not be obtained within this time limit, Time has expired. |
Gotchas
The process calling WinWaitEventSem must first obtain access to the semaphore in question or ERROR_INVALID_HANDLE will be returned. If the thread to be blocked, waiting on an event semaphore, is not a PM thread, DosWaitEventSem should be used instead of WinWaitEventSem.
Sample Code
#define INCL_WINMESSAGEMGR
#include <os2.h>
HEV hevMySemaphore; /* MySemaphore handle */
ULONG TimeOut= -1; /* the number of milliseconds the */
/* the caller will block for the sem */
/* this example will block forever */
APIRET rc; /* return code */
/* access is gained to the semaphore in question */
/* either by DosCreateEventSem ... */
/* ... or by DosOpenEventSem */
/* its handle is placed in hevMySemaphore */
rc = WinWaitEventSem(hevMySemaphore, TimeOut);
if (rc != 0)
{
/* We got an error to take care of. */
}
See Also
DosCloseEventSem, DosCreateEventSem, DosOpenEventSem, DosPostEventSem DosQueryEventSem, DosResetEventSem, DosWaitEventSem