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Diffstat (limited to 'nuttx/sched/pthread_condsignal.c')
-rw-r--r-- | nuttx/sched/pthread_condsignal.c | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/nuttx/sched/pthread_condsignal.c b/nuttx/sched/pthread_condsignal.c new file mode 100644 index 000000000..48ff4cf20 --- /dev/null +++ b/nuttx/sched/pthread_condsignal.c @@ -0,0 +1,137 @@ +/**************************************************************************** + * sched/pthread_condsignal.c + * + * Copyright (C) 2007-2009, 2012 Gregory Nutt. All rights reserved. + * Author: Gregory Nutt <gnutt@nuttx.org> + * + * 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 NuttX 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 <nuttx/config.h> + +#include <pthread.h> +#include <errno.h> +#include <debug.h> + +#include "pthread_internal.h" + +/**************************************************************************** + * Definitions + ****************************************************************************/ + +/**************************************************************************** + * Private Type Declarations + ****************************************************************************/ + +/**************************************************************************** + * Global Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Name: pthread_cond_signal + * + * Description: + * A thread can signal on a condition variable. + * + * Parameters: + * None + * + * Return Value: + * None + * + * Assumptions: + * + ****************************************************************************/ + +int pthread_cond_signal(FAR pthread_cond_t *cond) +{ + int ret = OK; + int sval; + + sdbg("cond=0x%p\n", cond); + + if (!cond) + { + ret = EINVAL; + } + else + { + /* Get the current value of the semaphore */ + + if (sem_getvalue((sem_t*)&cond->sem, &sval) != OK) + { + ret = EINVAL; + } + + /* If the value is less than zero (meaning that one or more + * thread is waiting), then post the condition semaphore. + * Only the highest priority waiting thread will get to execute + */ + + else + { + /* One of my objectives in this design was to make pthread_cond_signal + * usable from interrupt handlers. However, from interrupt handlers, + * you cannot take the associated mutex before signaling the condition. + * As a result, I think that there could be a race condition with + * the following logic which assumes that the if sval < 0 then the + * thread is waiting. Without the mutex, there is no atomic, protected + * operation that will guarantee this to be so. + */ + + sdbg("sval=%d\n", sval); + if (sval < 0) + { + sdbg("Signalling...\n"); + ret = pthread_givesemaphore((sem_t*)&cond->sem); + } + } + } + + sdbg("Returning %d\n", ret); + return ret; +} + + |