1 files changed, 141 insertions, 0 deletions
diff --git a/nuttx/sched/sem_trywait.c b/nuttx/sched/sem_trywait.c
new file mode 100644
index 0000000000..561ba0b444
--- /dev/null
+++ b/nuttx/sched/sem_trywait.c
@@ -0,0 +1,141 @@
+/************************************************************
+ * sem_trywait.c
+ *
+ *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ************************************************************/
+
+/************************************************************
+ * Included Files
+ ************************************************************/
+
+#include <sys/types.h>
+#include <semaphore.h>
+#include <sched.h>
+#include <errno.h>
+#include <nuttx/arch.h>
+#include "os_internal.h"
+#include "sem_internal.h"
+
+/************************************************************
+ * Compilation Switches
+ ************************************************************/
+
+/************************************************************
+ * Definitions
+ ************************************************************/
+
+/************************************************************
+ * Private Type Declarations
+ ************************************************************/
+
+/************************************************************
+ * Global Variables
+ ************************************************************/
+
+/************************************************************
+ * Private Variables
+ ************************************************************/
+
+/************************************************************
+ * Private Functions
+ ************************************************************/
+
+/************************************************************
+ * Public Functions
+ ************************************************************/
+
+/************************************************************
+ * Function: sem_trywait
+ *
+ * Description:
+ *   This function locks the specified semaphore only if the
+ *   semaphore is currently not locked.  Otherwise, it locks
+ *   the semaphore.  In either case, the call returns without
+ *   blocking.
+ *
+ * Parameters:
+ *   sem - the semaphore descriptor
+ *
+ * Return Value:
+ *   0 (OK) or -1 (ERROR) if unsuccessful
+ *   If this function returns -1 (ERROR), then the cause
+ *   of the failure will be reported in "errno" as:
+ *   - EINVAL:  Invalid attempt to get the semaphore
+ *   - EAGAIN:  The semaphore is not available.
+ *
+ * Assumptions:
+ *
+ ************************************************************/
+
+int sem_trywait(sem_t *sem)
+{
+  _TCB  *rtcb = (_TCB*)g_readytorun.head;
+  uint32 saved_state;
+  int    ret = ERROR;
+
+  /* Assume any errors reported are due to invalid arguments. */
+
+  *get_errno_ptr() = EINVAL;
+
+  if (sem)
+    {
+      /* The following operations must be performed with interrupts
+       * disabled because sem_post() may be called from an interrupt
+       * handler.
+       */
+
+      saved_state = irqsave();
+
+      /* Any further errors could only be occurred because the semaphore
+       * is not available.
+       */
+
+      *get_errno_ptr() = EAGAIN;
+
+      /* If the semaphore is available, give it to the requesting task */
+
+      if (sem->semcount > 0)
+        {
+          /* It is, let the task take the semaphore */
+
+          sem->semcount--;
+          rtcb->waitsem = NULL;
+          ret = OK;
+        }
+
+      /* Interrupts may now be enabled. */
+
+      irqrestore(saved_state);
+    }
+
+  return ret;
+}