CODEWITHSUNDEEP
c++multithreading
XWX
XWX

Reputation: 1997

Passing lock between thread

If I have the a workflow like the one below.

somelock;

thread1: somelock.lock();

thread1: ...

thread1: start thread2;

thread1: somelock.unlock();

      thread2 start : somelock.lock();
      thread2:...
      thread2: somelock.unlock();

With the condition that:

  1. only thread2 can acquire the lock after thread1 unlock.

  2. after thread2 unlock(), any one have access to somelock have a chance to acquire the lock.

As if the lock has been pass from thread1 to thread2. Is it achievable using C++?

Upvotes: 0

Views: 1006

Answers (1)

Joseph Artsimovich
Joseph Artsimovich

Reputation: 1519

only thread2 can acquire the lock after thread1 unlock.

Your pseudo-code doesn't guarantee the above condition. A mutex alone won't do the trick. A more complex approach is required:

std::mutex mtx;
std::condition_variable cond;
bool thread2_done = false;

void thread1()
{
    std::unique_lock<std::mutex> guard(mtx);

    // do some work with mtx locked

    start_thread2();
}

void thread2()
{
    std::unique_lock<std::mutex> guard(mtx);

    // do some work with mtx locked

    thread2_done = true;
    cond.notify_all();
}

void thread3()
{
    std::unique_lock<std::mutex> guard(mtx);
    cond.wait(guard, [] { return thread2_done; });

    // do some work with mtx locked
}

Upvotes: 1

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