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158 lines
5.5 KiB
158 lines
5.5 KiB
/* |
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Copyright (c) 2012, Broadcom Europe Ltd |
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All rights reserved. |
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Redistribution and use in source and binary forms, with or without |
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modification, are permitted provided that the following conditions are met: |
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* Redistributions of source code must retain the above copyright |
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notice, this list of conditions and the following disclaimer. |
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* Redistributions in binary form must reproduce the above copyright |
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notice, this list of conditions and the following disclaimer in the |
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documentation and/or other materials provided with the distribution. |
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* Neither the name of the copyright holder nor the |
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names of its contributors may be used to endorse or promote products |
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derived from this software without specific prior written permission. |
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND |
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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED |
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE |
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY |
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DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND |
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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*/ |
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/*============================================================================= |
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VideoCore OS Abstraction Layer - public header file |
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=============================================================================*/ |
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#ifndef VCOS_SEMAPHORE_H |
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#define VCOS_SEMAPHORE_H |
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#ifdef __cplusplus |
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extern "C" { |
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#endif |
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#include "interface/vcos/vcos_types.h" |
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#ifndef VCOS_PLATFORM_H |
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#include "vcos.h" |
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#endif |
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/** |
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* \file vcos_semaphore.h |
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* |
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* \section sem Semaphores |
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* |
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* This provides counting semaphores. Semaphores are not re-entrant. On sensible |
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* operating systems a semaphore can always be posted but can only be taken in |
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* thread (not interrupt) context. Under Nucleus, a LISR cannot post a semaphore, |
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* although it would not be hard to lift this restriction. |
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* |
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* \subsection timeout Timeout |
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* |
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* On both Nucleus and ThreadX a semaphore can be taken with a timeout. This is |
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* not supported by VCOS because it makes the non-timeout code considerably more |
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* complicated (and hence slower). In the unlikely event that you need a timeout |
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* with a semaphore, and you cannot simply redesign your code to avoid it, use |
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* an event flag (vcos_event_flags.h). |
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* |
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* \subsection sem_nucleus Changes from Nucleus: |
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* |
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* Semaphores are always "FIFO" - i.e. sleeping threads are woken in FIFO order. That's |
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* because: |
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* \arg there's no support for NU_PRIORITY in threadx (though it can be emulated, slowly) |
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* \arg we don't appear to actually consciously use it - for example, Dispmanx uses |
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* it, but all threads waiting are the same priority. |
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* |
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*/ |
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/** |
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* \brief Create a semaphore. |
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* |
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* Create a semaphore. |
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* |
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* @param sem Pointer to memory to be initialized |
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* @param name A name for this semaphore. The name may be truncated internally. |
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* @param count The initial count for the semaphore. |
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* |
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* @return VCOS_SUCCESS if the semaphore was created. |
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* |
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*/ |
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VCOS_INLINE_DECL |
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VCOS_STATUS_T vcos_semaphore_create(VCOS_SEMAPHORE_T *sem, const char *name, VCOS_UNSIGNED count); |
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/** |
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* \brief Wait on a semaphore. |
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* |
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* There is no timeout option on a semaphore, as adding this will slow down |
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* implementations on some platforms. If you need that kind of behaviour, use |
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* an event group. |
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* |
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* On most platforms this always returns VCOS_SUCCESS, and so would ideally be |
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* a void function, however some platforms allow a wait to be interrupted so |
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* it remains non-void. |
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* |
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* @param sem Semaphore to wait on |
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* @return VCOS_SUCCESS - semaphore was taken. |
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* VCOS_EAGAIN - could not take semaphore |
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* |
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*/ |
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VCOS_INLINE_DECL |
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VCOS_STATUS_T vcos_semaphore_wait(VCOS_SEMAPHORE_T *sem); |
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/** |
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* \brief Wait on a semaphore with a timeout. |
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* |
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* Note that this function may not be implemented on all |
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* platforms, and may not be efficient on all platforms |
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* (see comment in vcos_semaphore_wait) |
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* |
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* Try to obtain the semaphore. If it is already taken, return |
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* VCOS_EAGAIN. |
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* @param sem Semaphore to wait on |
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* @param timeout Number of milliseconds to wait before |
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* returning if the semaphore can't be acquired. |
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* @return VCOS_SUCCESS - semaphore was taken. |
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* VCOS_EAGAIN - could not take semaphore (i.e. timeout |
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* expired) |
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* VCOS_EINVAL - Some other error (most likely bad |
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* parameters). |
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*/ |
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VCOS_INLINE_DECL |
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VCOS_STATUS_T vcos_semaphore_wait_timeout(VCOS_SEMAPHORE_T *sem, VCOS_UNSIGNED timeout); |
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/** |
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* \brief Try to wait for a semaphore. |
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* |
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* Try to obtain the semaphore. If it is already taken, return VCOS_TIMEOUT. |
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* @param sem Semaphore to wait on |
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* @return VCOS_SUCCESS - semaphore was taken. |
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* VCOS_EAGAIN - could not take semaphore |
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*/ |
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VCOS_INLINE_DECL |
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VCOS_STATUS_T vcos_semaphore_trywait(VCOS_SEMAPHORE_T *sem); |
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/** |
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* \brief Post a semaphore. |
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* |
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* @param sem Semaphore to wait on |
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*/ |
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VCOS_INLINE_DECL |
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VCOS_STATUS_T vcos_semaphore_post(VCOS_SEMAPHORE_T *sem); |
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/** |
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* \brief Delete a semaphore, releasing any resources consumed by it. |
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* |
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* @param sem Semaphore to wait on |
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*/ |
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VCOS_INLINE_DECL |
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void vcos_semaphore_delete(VCOS_SEMAPHORE_T *sem); |
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#ifdef __cplusplus |
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} |
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#endif |
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#endif |
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