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143 lines
4.3 KiB
C
143 lines
4.3 KiB
C
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//---------------------------------------------------------
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// For conditions of distribution and use, see
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// https://github.com/preshing/cpp11-on-multicore/blob/master/LICENSE
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//---------------------------------------------------------
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#ifndef __CPP11OM_BENAPHORE_H__
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#define __CPP11OM_BENAPHORE_H__
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#include <cassert>
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#include <thread>
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#include <atomic>
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#include "sema.h"
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//---------------------------------------------------------
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// NonRecursiveBenaphore
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//---------------------------------------------------------
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class NonRecursiveBenaphore
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{
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private:
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std::atomic<int> m_contentionCount;
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DefaultSemaphoreType m_sema;
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public:
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NonRecursiveBenaphore() : m_contentionCount(0) {}
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void lock()
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{
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if (m_contentionCount.fetch_add(1, std::memory_order_acquire) > 0)
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{
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m_sema.wait();
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}
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}
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bool tryLock()
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{
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if (m_contentionCount.load(std::memory_order_relaxed) != 0)
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return false;
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int expected = 0;
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return m_contentionCount.compare_exchange_strong(expected, 1, std::memory_order_acquire);
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}
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void unlock()
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{
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int oldCount = m_contentionCount.fetch_sub(1, std::memory_order_release);
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assert(oldCount > 0);
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if (oldCount > 1)
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{
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m_sema.signal();
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}
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}
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};
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//---------------------------------------------------------
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// RecursiveBenaphore
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//---------------------------------------------------------
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class RecursiveBenaphore
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{
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private:
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std::atomic<int> m_contentionCount;
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std::atomic<std::thread::id> m_owner;
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int m_recursion;
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DefaultSemaphoreType m_sema;
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public:
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RecursiveBenaphore()
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: m_contentionCount(0)
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// Apple LLVM 6.0 (in Xcode 6.1) refuses to initialize m_owner from a std::thread::id.
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// "error: no viable conversion from 'std::__1::__thread_id' to '_Atomic(std::__1::__thread_id)'"
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// (Note: On Linux, as of April 11, 2015, Clang 3.7 & libc++ don't have this problem.)
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// Prefer atomic_init (below) when Apple LLVM is detected.
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#if !(defined(__llvm__) && defined(__APPLE__))
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, m_owner(std::thread::id())
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#endif
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, m_recursion(0)
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{
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// GCC 4.7.2's libstdc++-v3 doesn't implement atomic_init.
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// "warning: inline function 'void std::atomic_init(std::atomic<_ITp>*, _ITp) [with _ITp = std::thread::id]' used but never defined [enabled by default]"
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// Using the constructor (above) in that case.
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#if (defined(__llvm__) && defined(__APPLE__))
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std::atomic_init(&m_owner, std::thread::id());
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#endif
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// If this assert fails on your system, you'll have to replace std::thread::id with a
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// more compact, platform-specific thread ID, or just comment the assert and live with
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// the extra overhead.
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assert(m_owner.is_lock_free());
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}
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void lock()
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{
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std::thread::id tid = std::this_thread::get_id();
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if (m_contentionCount.fetch_add(1, std::memory_order_acquire) > 0)
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{
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if (tid != m_owner.load(std::memory_order_relaxed))
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m_sema.wait();
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}
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//--- We are now inside the lock ---
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m_owner.store(tid, std::memory_order_relaxed);
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m_recursion++;
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}
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bool tryLock()
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{
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std::thread::id tid = std::this_thread::get_id();
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if (m_owner.load(std::memory_order_relaxed) == tid)
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{
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// Already inside the lock
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m_contentionCount.fetch_add(1, std::memory_order_relaxed);
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}
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else
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{
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if (m_contentionCount.load(std::memory_order_relaxed) != 0)
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return false;
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int expected = 0;
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if (!m_contentionCount.compare_exchange_strong(expected, 1, std::memory_order_acquire))
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return false;
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//--- We are now inside the lock ---
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m_owner.store(tid, std::memory_order_relaxed);
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}
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m_recursion++;
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return true;
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}
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void unlock()
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{
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assert(std::this_thread::get_id() == m_owner.load(std::memory_order_relaxed));
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int recur = --m_recursion;
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if (recur == 0)
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m_owner.store(std::thread::id(), std::memory_order_relaxed);
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if (m_contentionCount.fetch_sub(1, std::memory_order_release) > 1)
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{
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if (recur == 0)
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m_sema.signal();
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}
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//--- We are now outside the lock ---
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}
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};
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#endif // __CPP11OM_BENAPHORE_H__
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