rom/exec/attemptsemaphoreshared.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Try to lock a semaphore shared.
   6     Lang: english
   7 */
   8 #include "exec_intern.h"
   9 #include "semaphores.h"
  10 #include <exec/semaphores.h>
  11 #include <proto/exec.h>
  12
  13 #define CHECK_INITSEM 1
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18
  19         AROS_LH1(ULONG, AttemptSemaphoreShared,
  20
  21 /*  SYNOPSIS */
  22         AROS_LHA(struct SignalSemaphore *, sigSem, A0),
  23
  24 /*  LOCATION */
  25         struct ExecBase *, SysBase, 120, Exec)
  26
  27 /*  FUNCTION
  28         Tries to get a shared lock on a signal semaphore. If the lock cannot
  29         be obtained false is returned. There may be more than one shared lock
  30         at a time but an exclusive lock prevents all other locks. The lock
  31         must be released with ReleaseSemaphore().
  32
  33     INPUTS
  34         sigSem - pointer to semaphore structure
  35
  36     RESULT
  37         True if the semaphore could be obtained, false otherwise.
  38
  39     NOTES
  40
  41     EXAMPLE
  42
  43     BUGS
  44
  45     SEE ALSO
  46         ReleaseSemaphore()
  47
  48     INTERNALS
  49
  50 *****************************************************************************/
  51 {
  52     AROS_LIBFUNC_INIT
  53
  54     struct Task *me = FindTask(NULL);
  55     ULONG retval = TRUE;
  56
  57 #if CHECK_INITSEM
  58     if (sigSem->ss_Link.ln_Type != NT_SIGNALSEM)
  59     {
  60         kprintf("\n\nAttemptSemaphoreShared called on an unintialized semaphore!!! "
  61                 "sem = %x  task = %x (%s)\n\n", sigSem, me, me->tc_Node.ln_Name);
  62     }
  63 #endif
  64
  65     /* Protect the semaphore structure */
  66     Forbid();
  67
  68     /* Increment the queue count. This will need SMP protection */
  69     sigSem->ss_QueueCount++;
  70
  71     if( sigSem->ss_QueueCount == 0 )
  72     {
  73         /* The semaphore wasn't owned. We can now own it */
  74         sigSem->ss_Owner = NULL;
  75         sigSem->ss_NestCount++;
  76     }
  77     else if( ( sigSem->ss_Owner == me ) || ( sigSem->ss_Owner == NULL ) )
  78     {
  79         /* The semaphore was owned by me or is shared, just increase the nest count */
  80         sigSem->ss_NestCount++;
  81     }
  82     else
  83     {
  84         /* We can't get ownership, just return it. */
  85         sigSem->ss_QueueCount--;
  86         retval = FALSE;
  87     }
  88
  89     /* All done. */
  90     Permit();
  91
  92     return retval;
  93
  94     AROS_LIBFUNC_EXIT
  95 } /* AttemptSemaphoreShared */