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c++linuxmacosspinwait
Coder
Coder

Reputation: 451

What is the equivalent of Windows .NET (C++) SpinWait on Linux and Mac OS X?

Windows .NET (C++) provides SpinWait for Hyper-threading friendly busy waiting with YIELD/PAUSE instructions. What is the equivalent function on Linux and Mac OS X? If a system call isn't available, how can an equivalent be implemented in user space?

See Windows Thread::SpinWait

See Long Duration Spin-wait Loops on Hyper-Threading Technology Enabled Intel Processors for a discussion of performance issues with spin waits.

Upvotes: 2

Views: 754

Answers (1)

ergohack
ergohack

Reputation: 1358

See https://www.codeproject.com/articles/184046/spin-lock-in-c by sameer_87

#include "SpinLock.h"
#include <iostream>

using namespace LockFree;
using namespace std;

void tSpinWait::Lock(tSpinLock &LockObj)
{
    m_iterations = 0;
    while(true)
    {
        // A thread alreading owning the lock shouldn't be allowed to wait to acquire the lock - reentrant safe
        if(LockObj.dest == GetCurrentThreadId())
            break;
        /*
          Spinning in a loop of interlockedxxx calls can reduce the available memory bandwidth and slow
          down the rest of the system. Interlocked calls are expensive in their use of the system memory
          bus. It is better to see if the 'dest' value is what it is expected and then retry interlockedxx.
        */
        if(InterlockedCompareExchange(&LockObj.dest, LockObj.exchange, LockObj.compare) == 0)
        {
            //assign CurrentThreadId to dest to make it re-entrant safe
            LockObj.dest = GetCurrentThreadId();
            // lock acquired 
            break;          
        }

        // spin wait to acquire 
        while(LockObj.dest != LockObj.compare)
        {
            if(HasThreasholdReached())
            {
                if(m_iterations + YIELD_ITERATION >= MAX_SLEEP_ITERATION)
                    Sleep(0);

                if(m_iterations >= YIELD_ITERATION && m_iterations < MAX_SLEEP_ITERATION)
                {
                    m_iterations = 0;
                    SwitchToThread();
                }
            }
            // Yield processor on multi-processor but if on single processor then give other thread the CPU
            m_iterations++;
            if(Helper::GetNumberOfProcessors() > 1) { YieldProcessor(/*no op*/); }
            else { SwitchToThread(); }              
        }               
    }
}
//

void tSpinWait::Unlock(tSpinLock &LockObj)
{
    if(LockObj.dest != GetCurrentThreadId())
        throw std::runtime_error("Unexpected thread-id in release");
    // lock released
    InterlockedCompareExchange(&LockObj.dest, LockObj.compare, GetCurrentThreadId());   
}

Upvotes: 0

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