rom/exec/attemptsemaphore.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Try to lock a sempahore.
   6     Lang: english
   7 */
   8 #include "exec_intern.h"
   9 #include <exec/semaphores.h>
  10 #include <proto/exec.h>
  11
  12 #define CHECK_INITSEM 1
  13
  14 /*****************************************************************************
  15
  16     NAME */
  17
  18         AROS_LH1(ULONG, AttemptSemaphore,
  19
  20 /*  SYNOPSIS */
  21         AROS_LHA(struct SignalSemaphore *, sigSem, A0),
  22
  23 /*  LOCATION */
  24         struct ExecBase *, SysBase, 96, Exec)
  25
  26 /*  FUNCTION
  27         Tries to get an exclusive lock on a signal semaphore. If the semaphore
  28         is already in use by another task, this function does not wait but
  29         returns false instead.
  30
  31     INPUTS
  32         sigSem - Pointer so semaphore structure.
  33
  34     RESULT
  35         TRUE if the semaphore could be obtained, FALSE otherwise.
  36
  37     NOTES
  38         The lock must be freed with ReleaseSemaphore().
  39
  40     EXAMPLE
  41
  42     BUGS
  43
  44     SEE ALSO
  45         ReleaseSemaphore()
  46
  47     INTERNALS
  48
  49 *****************************************************************************/
  50 {
  51     AROS_LIBFUNC_INIT
  52
  53     struct Task *me = FindTask(NULL);
  54
  55 #if CHECK_INITSEM
  56     if (sigSem->ss_Link.ln_Type != NT_SIGNALSEM)
  57     {
  58         kprintf("\n\nAttemptSemaphore called on an uninitialized semaphore!!! "
  59                 "sem = %x  task = %x (%s)\n\n", sigSem, me, me->tc_Node.ln_Name);
  60     }
  61 #endif
  62
  63     /* Arbitrate for semaphore nesting count and owner fields */
  64     Forbid();
  65
  66     /*
  67         We are going to lock or fail, so we increment the
  68         ss_QueueCount anyway. We shall fix it up later if it was
  69         wrong.
  70     */
  71     sigSem->ss_QueueCount++;
  72
  73     /*  If it is now equal to zero, then we have got it */
  74     if( sigSem->ss_QueueCount == 0 )
  75     {
  76         sigSem->ss_Owner = me;
  77         sigSem->ss_NestCount++;
  78     }
  79     /*  It was already owned by me, so lets just inc the nest count */
  80     else if( sigSem->ss_Owner == me )
  81     {
  82         sigSem->ss_NestCount++;
  83     }
  84
  85     /*  Owned by somebody else, we fix up the owner count. */
  86     else
  87     {
  88         sigSem->ss_QueueCount--;
  89     }
  90
  91     Permit();
  92
  93     /*
  94         We own the semaphore if it is owned by me
  95     */
  96     return (sigSem->ss_Owner == me ? TRUE : FALSE);
  97
  98     AROS_LIBFUNC_EXIT
  99 } /* AttemptSemaphore */