/**************************************************************************** * libs/libc/misc/lib_filesem.c * * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. The * ASF licenses this file to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance with the * License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations * under the License. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include "libc.h" #ifndef CONFIG_STDIO_DISABLE_BUFFERING /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * lib_sem_initialize ****************************************************************************/ void lib_sem_initialize(FAR struct file_struct *stream) { /* Initialize the LIB semaphore to one (to support one-at-a-time access * to private data sets. */ _SEM_INIT(&stream->fs_sem, 0, 1); stream->fs_holder = -1; stream->fs_counts = 0; } /**************************************************************************** * lib_take_semaphore ****************************************************************************/ void lib_take_semaphore(FAR struct file_struct *stream) { pid_t my_pid = getpid(); int ret; /* Do I already have the semaphore? */ if (stream->fs_holder == my_pid) { /* Yes, just increment the number of references that I have */ stream->fs_counts++; } else { /* Take the semaphore (perhaps waiting) */ while ((ret = _SEM_WAIT(&stream->fs_sem)) < 0) { /* The only case that an error should occr here is if the wait * was awakened by a signal. */ DEBUGASSERT(_SEM_ERRNO(ret) == EINTR || _SEM_ERRNO(ret) == ECANCELED); UNUSED(ret); } /* We have it. Claim the stak and return */ stream->fs_holder = my_pid; stream->fs_counts = 1; } } /**************************************************************************** * lib_give_semaphore ****************************************************************************/ void lib_give_semaphore(FAR struct file_struct *stream) { /* I better be holding at least one reference to the semaphore */ DEBUGASSERT(stream->fs_holder == getpid()); /* Do I hold multiple references to the semphore */ if (stream->fs_counts > 1) { /* Yes, just release one count and return */ stream->fs_counts--; } else { /* Nope, this is the last reference I have */ stream->fs_holder = -1; stream->fs_counts = 0; DEBUGVERIFY(_SEM_POST(&stream->fs_sem)); } } #endif /* CONFIG_STDIO_DISABLE_BUFFERING */