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94 lines
2.6 KiB
C++
94 lines
2.6 KiB
C++
/*
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* Semaphore.h - Semaphore declaration
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*
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* Copyright (c) 2022-2022 Johannes Lorenz <jlsf2013$users.sourceforge.net, $=@>
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*
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* This file is part of LMMS - https://lmms.io
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program (see COPYING); if not, write to the
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* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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* Boston, MA 02110-1301 USA.
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*
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*/
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/*
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* This code has been copied and adapted from https://github.com/drobilla/jalv
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* File src/zix/sem.h
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*/
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#ifndef LMMS_SEMAPHORE_H
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#define LMMS_SEMAPHORE_H
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#include "lmmsconfig.h"
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#ifdef LMMS_BUILD_APPLE
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# include <mach/mach.h>
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#elif defined(LMMS_BUILD_WIN32)
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# include <windows.h>
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#else
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# include <semaphore.h>
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#endif
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#include <system_error>
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namespace lmms {
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/**
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A counting semaphore.
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This is an integer that is always positive, and has two main operations:
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increment (post) and decrement (wait). If a decrement can not be performed
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(i.e. the value is 0) the caller will be blocked until another thread posts
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and the operation can succeed.
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Semaphores can be created with any starting value, but typically this will
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be 0 so the semaphore can be used as a simple signal where each post
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corresponds to one wait.
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Semaphores are very efficient (much moreso than a mutex/cond pair). In
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particular, at least on Linux, post is async-signal-safe, which means it
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does not block and will not be interrupted. If you need to signal from
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a realtime thread, this is the most appropriate primitive to use.
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@note Likely outdated with C++20's std::counting_semaphore
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(though we have to check that this will be RT conforming on all platforms)
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*/
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class Semaphore
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{
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public:
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Semaphore(unsigned initial);
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Semaphore(const Semaphore&) = delete;
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Semaphore& operator=(const Semaphore&) = delete;
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Semaphore(Semaphore&&) = delete;
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Semaphore& operator=(Semaphore&&) = delete;
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~Semaphore();
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void post();
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void wait();
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bool tryWait();
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private:
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#ifdef LMMS_BUILD_APPLE
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semaphore_t m_sem;
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#elif defined(LMMS_BUILD_WIN32)
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HANDLE m_sem;
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#else
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sem_t m_sem;
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#endif
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};
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} // namespace lmms
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#endif // LMMS_SEMAPHORE_H
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