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- /*
- (C) 1995-96 AROS - The Amiga Replacement OS
- $Id: obtainsemaphoreshared.c,v 1.7 1997/01/01 03:46:12 ldp Exp $
- $Log: obtainsemaphoreshared.c,v $
- Revision 1.7 1997/01/01 03:46:12 ldp
- Committed Amiga native (support) code
-
- Changed clib to proto
-
- Revision 1.6 1996/12/10 13:51:49 aros
- Moved all #include's in the first column so makedepend can see it.
-
- Revision 1.5 1996/10/24 15:50:52 aros
- Use the official AROS macros over the __AROS versions.
-
- Revision 1.4 1996/08/13 13:56:04 digulla
- Replaced AROS_LA by AROS_LHA
- Replaced some AROS_LH*I by AROS_LH*
- Sorted and added includes
-
- Revision 1.3 1996/08/01 17:41:14 digulla
- Added standard header for all files
-
- Desc:
- Lang: english
- */
- #include "exec_intern.h"
- #include "semaphores.h"
- #include <exec/semaphores.h>
- #include <proto/exec.h>
-
- /*****************************************************************************
-
- NAME */
-
- AROS_LH1(void, ObtainSemaphoreShared,
-
- /* SYNOPSIS */
- AROS_LHA(struct SignalSemaphore *, sigSem, A0),
-
- /* LOCATION */
- struct ExecBase *, SysBase, 113, Exec)
-
- /* FUNCTION
- Get a shared lock on a semaphore. If the lock cannot be obtained
- immediately this function waits. There may be more than one shared
- locks at the same time but only one exclusive one. An exclusive
- lock prevents shared locks. Shared locks are released with
- ReleaseSemaphore().
-
- INPUTS
- sigSem - Pointer to semaphore structure
-
- RESULT
-
- NOTES
- This function preserves all registers.
-
- EXAMPLE
-
- BUGS
-
- SEE ALSO
- ReleaseSemaphore()
-
- INTERNALS
-
- HISTORY
- 29-10-95 digulla automatically created from
- exec_lib.fd and clib/exec_protos.h
- 21-01-96 fleischer implementation
-
- *****************************************************************************/
- {
- AROS_LIBFUNC_INIT
- AROS_LIBBASE_EXT_DECL(struct ExecBase *,SysBase)
- struct Task *me;
-
- /* Get pointer to current task */
- me=SysBase->ThisTask;
-
- /* Arbitrate for the semaphore structure */
- Forbid();
-
- /* Check if there's an exclusive lock on the semaphore */
- if(sigSem->ss_NestCount>0)
- {
- /* Yes. Is it owned by the current task? */
- if(sigSem->ss_Owner!=me)
- {
- /* No. Prepare a node for the waiting queue. */
- struct SemaphoreNode sn;
- sn.node.ln_Pri =SN_TYPE_OBTAIN;
- sn.node.ln_Name=(char *)SM_SHARED;
- sn.task =me;
-
- /* Add it. */
- AddTail((struct List *)&sigSem->ss_WaitQueue,&sn.node);
-
- /* Wait until the semaphore is free */
- Wait(SEMAPHORESIGF);
-
- /* ss_NestCount and ss_Owner are already set by ReleaseSemaphore() */
- }else
- /* Add one nesting level more */
- sigSem->ss_NestCount++;
- }else
- {
- /* There's no exclusive lock on the semaphore. Get a shared one. */
- sigSem->ss_NestCount--;
-
- /* Invalidate the owner field - so no task may think this semaphore is his. */
- sigSem->ss_Owner=NULL;
- }
-
- /* All done. */
- Permit();
- AROS_LIBFUNC_EXIT
- } /* ObtainSemaphoreShared */
-
-