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186ca9c235
Beast includes a lot of code for encapsulating cross-platform differences which are not used or needed by rippled. Additionally, a lot of that code implements functionality that is available from the standard library. This moves away from custom implementations of features that the standard library provides and reduces the number of platform-specific interfaces andfeatures that Beast makes available. Highlights include: * Use std:: instead of beast implementations when possible * Reduce the use of beast::String in public interfaces * Remove Windows-specific COM and Registry code * Reduce the public interface of beast::File * Reduce the public interface of beast::SystemStats * Remove unused sysctl/getsysinfo functions * Remove beast::Logger
120 lines
3.7 KiB
C++
120 lines
3.7 KiB
C++
//------------------------------------------------------------------------------
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/*
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This file is part of Beast: https://github.com/vinniefalco/Beast
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Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
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Portions of this file are from JUCE.
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Copyright (c) 2013 - Raw Material Software Ltd.
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Please visit http://www.juce.com
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Permission to use, copy, modify, and/or distribute this software for any
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purpose with or without fee is hereby granted, provided that the above
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copyright notice and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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ANY SPECIAL , DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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//==============================================================================
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#ifndef BEAST_THREADS_SPINLOCK_H_INCLUDED
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#define BEAST_THREADS_SPINLOCK_H_INCLUDED
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#include <beast/threads/UnlockGuard.h>
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#include <atomic>
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#include <mutex>
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#include <thread>
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namespace beast {
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//==============================================================================
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/**
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A simple spin-lock class that can be used as a simple, low-overhead mutex for
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uncontended situations.
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Note that unlike a CriticalSection, this type of lock is not re-entrant, and may
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be less efficient when used it a highly contended situation, but it's very small and
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requires almost no initialisation.
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It's most appropriate for simple situations where you're only going to hold the
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lock for a very brief time.
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@see CriticalSection
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*/
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class SpinLock
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{
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public:
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/** Provides the type of scoped lock to use for locking a SpinLock. */
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typedef std::lock_guard <SpinLock> ScopedLockType;
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/** Provides the type of scoped unlocker to use with a SpinLock. */
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typedef UnlockGuard <SpinLock> ScopedUnlockType;
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SpinLock()
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: m_lock (0)
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{
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}
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~SpinLock() = default;
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SpinLock (SpinLock const&) = delete;
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SpinLock& operator= (SpinLock const&) = delete;
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/** Attempts to acquire the lock, returning true if this was successful. */
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inline bool tryEnter() const noexcept
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{
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return (m_lock.exchange (1) == 0);
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}
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/** Acquires the lock.
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This will block until the lock has been successfully acquired by this thread.
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Note that a SpinLock is NOT re-entrant, and is not smart enough to know whether the
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caller thread already has the lock - so if a thread tries to acquire a lock that it
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already holds, this method will never return!
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It's strongly recommended that you never call this method directly - instead use the
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ScopedLockType class to manage the locking using an RAII pattern instead.
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*/
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void enter() const noexcept
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{
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if (! tryEnter())
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{
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for (int i = 20; --i >= 0;)
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{
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if (tryEnter())
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return;
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}
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while (! tryEnter())
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std::this_thread::yield ();
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}
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}
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/** Releases the lock. */
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inline void exit() const noexcept
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{
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// Agh! Releasing a lock that isn't currently held!
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bassert (m_lock.load () == 1);
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m_lock.store (0);
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}
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void lock () const
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{ enter(); }
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void unlock () const
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{ exit(); }
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bool try_lock () const
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{ return tryEnter(); }
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private:
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mutable std::atomic<int> m_lock;
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};
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}
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#endif
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