/**************************************************************************** * sched/semaphore/sem_wait.c * * Copyright (C) 2007-2013, 2016 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * 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 #include #include #include #include #include #include #include #include "sched/sched.h" #include "semaphore/semaphore.h" /**************************************************************************** * 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 struct tcb_s *rtcb = this_task(); irqstate_t flags; int ret = ERROR; /* This API should not be called from interrupt handlers */ DEBUGASSERT(sem != NULL && up_interrupt_context() == false); /* The following operations must be performed with interrupts * disabled because sem_post() may be called from an interrupt * handler. */ flags = enter_critical_section(); /* sem_wait() is a cancellation point */ if (enter_cancellation_point()) { #ifdef CONFIG_CANCELLATION_POINTS /* If there is a pending cancellation, then do not perform * the wait. Exit now with ECANCELED. */ set_errno(ECANCELED); leave_cancellation_point(); leave_critical_section(flags); return ERROR; #endif } /* Make sure we were supplied with a valid semaphore. */ if (sem != NULL) { /* 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 */ ASSERT(rtcb->waitsem == NULL); /* 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 */ set_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 (get_errno() != EINTR && get_errno() != ETIMEDOUT) { /* Not awakened by a signal or a timeout... * * NOTE that in this case sem_addholder() was called by logic * in sem_wait() fore this thread was restarted. */ ret = OK; } #ifdef CONFIG_PRIORITY_INHERITANCE sched_unlock(); #endif } } else { set_errno(EINVAL); } leave_cancellation_point(); leave_critical_section(flags); return ret; }