8778fea0bb
This eliminates portability issues among platforms that don't have a pthreads implementation. Differential Revision: http://reviews.llvm.org/D12043 Reviewed By: Greg Clayton llvm-svn: 245234
81 lines
2.4 KiB
C++
81 lines
2.4 KiB
C++
#include <stdlib.h>
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#include <stdio.h>
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#include <condition_variable>
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#include <mutex>
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#include <thread>
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std::mutex contended_mutex;
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std::mutex control_mutex;
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std::mutex thread_started_mutex;
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std::unique_lock<std::mutex> *contended_lock = nullptr;
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std::unique_lock<std::mutex> *control_lock = nullptr;
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std::unique_lock<std::mutex> *thread_started_lock = nullptr;
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std::condition_variable control_condition;
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std::condition_variable thread_started_condition;
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// This function runs in a thread. The locking dance is to make sure that
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// by the time the main thread reaches the pthread_join below, this thread
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// has for sure acquired the contended_mutex. So then the call_me_to_get_lock
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// function will block trying to get the mutex, and only succeed once it
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// signals this thread, then lets it run to wake up from the cond_wait and
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// release the mutex.
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void *
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lock_acquirer_1 ()
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{
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contended_lock->lock();
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// Grab this mutex, that will ensure that the main thread
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// is in its cond_wait for it (since that's when it drops the mutex.
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thread_started_lock->lock();
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thread_started_lock->unlock();
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// Now signal the main thread that it can continue, we have the contended lock
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// so the call to call_me_to_get_lock won't make any progress till this
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// thread gets a chance to run.
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control_lock->lock();
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thread_started_condition.notify_all();
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control_condition.wait(*control_lock);
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return NULL;
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}
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int
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call_me_to_get_lock ()
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{
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control_condition.notify_all();
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contended_lock->lock();
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return 567;
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}
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int main ()
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{
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contended_lock = new std::unique_lock<std::mutex>(contended_mutex, std::defer_lock);
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control_lock = new std::unique_lock<std::mutex>(control_mutex, std::defer_lock);
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thread_started_lock = new std::unique_lock<std::mutex>(thread_started_mutex, std::defer_lock);
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thread_started_lock->lock();
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std::thread thread_1(lock_acquirer_1);
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thread_started_condition.wait(*thread_started_lock);
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control_lock->lock();
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control_lock->unlock();
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// Break here. At this point the other thread will have the contended_mutex,
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// and be sitting in its cond_wait for the control condition. So there is
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// no way that our by-hand calling of call_me_to_get_lock will proceed
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// without running the first thread at least somewhat.
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call_me_to_get_lock();
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thread_1.join();
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return 0;
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}
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