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Diffstat (limited to 'nuttx/sched/sem_wait.c')
| -rw-r--r-- | nuttx/sched/sem_wait.c | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/nuttx/sched/sem_wait.c b/nuttx/sched/sem_wait.c new file mode 100644 index 000000000..9dfbaa6c3 --- /dev/null +++ b/nuttx/sched/sem_wait.c @@ -0,0 +1,216 @@ +/**************************************************************************** + * sched/sem_wait.c + * + * Copyright (C) 2007-2012 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 <stdbool.h> +#include <semaphore.h> +#include <errno.h> +#include <assert.h> +#include <nuttx/arch.h> + +#include "os_internal.h" +#include "sem_internal.h" + +/**************************************************************************** + * Pre-processor Definitions + ****************************************************************************/ + +/**************************************************************************** + * Private Type Declarations + ****************************************************************************/ + +/**************************************************************************** + * Global Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Name: sem_wait + * + * Description: + * This function attempts to lock the semaphore referenced by 'sem'. If + * the semaphore value is (<=) zero, then the calling task will not return + * until it successfully acquires the lock. + * + * Parameters: + * sem - Semaphore descriptor. + * + * Return Value: + * 0 (OK), or -1 (ERROR) is 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 + * - EINTR: The wait was interrupted by the receipt of a signal. + * + * Assumptions: + * + ****************************************************************************/ + +int sem_wait(FAR sem_t *sem) +{ + FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head; + int ret = ERROR; + irqstate_t saved_state; + + /* This API should not be called from interrupt handlers */ + + DEBUGASSERT(up_interrupt_context() == false) + + /* Assume any errors reported are due to invalid arguments. */ + + errno = 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(); + + /* Check if the lock is available */ + + if (sem->semcount > 0) + { + /* It is, let the task take the semaphore. */ + + sem->semcount--; + sem_addholder(sem); + rtcb->waitsem = NULL; + ret = OK; + } + + /* The semaphore is NOT available, We will have to block the + * current thread of execution. + */ + + else + { + /* First, verify that the task is not already waiting on a + * semaphore + */ + + if (rtcb->waitsem != NULL) + { + PANIC(OSERR_BADWAITSEM); + } + + /* Handle the POSIX semaphore (but don't set the owner yet) */ + + sem->semcount--; + + /* Save the waited on semaphore in the TCB */ + + rtcb->waitsem = sem; + + /* If priority inheritance is enabled, then check the priority of + * the holder of the semaphore. + */ + +#ifdef CONFIG_PRIORITY_INHERITANCE + /* Disable context switching. The following operations must be + * atomic with regard to the scheduler. + */ + + sched_lock(); + + /* Boost the priority of any threads holding a count on the + * semaphore. + */ + + sem_boostpriority(sem); +#endif + /* Add the TCB to the prioritized semaphore wait queue */ + + errno = 0; + up_block_task(rtcb, TSTATE_WAIT_SEM); + + /* When we resume at this point, either (1) the semaphore has been + * assigned to this thread of execution, or (2) the semaphore wait + * has been interrupted by a signal or a timeout. We can detect these + * latter cases be examining the errno value. + * + * In the event that the semaphore wait was interrupted by a signal or + * a timeout, certain semaphore clean-up operations have already been + * performed (see sem_waitirq.c). Specifically: + * + * - sem_canceled() was called to restore the priority of all threads + * that hold a reference to the semaphore, + * - The semaphore count was decremented, and + * - tcb->waitsem was nullifed. + * + * It is necesaary to do these things in sem_waitirq.c because a long + * time may elapse between the time that the signal was issued and + * this thread is awakened and this leaves a door open to several + * race conditions. + */ + + if (errno != EINTR && errno != ETIMEDOUT) + { + /* Not awakened by a signal or a timeout... We hold the semaphore */ + + sem_addholder(sem); + ret = OK; + } + +#ifdef CONFIG_PRIORITY_INHERITANCE + sched_unlock(); +#endif + } + + /* Interrupts may now be enabled. */ + + irqrestore(saved_state); + } + + return ret; +} |