http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53830
Bug #: 53830
Summary: condition_variable_any - deadlock issue
Classification: Unclassified
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: m_rei...@informatik.uni-kl.de
Created attachment 27730
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27730
Simple test program that causes deadlock
I believe there is a bug (or a pitfall at least) in std::condition_variable_any
that can cause deadlocks. Actually, one of my programs just froze because of
this.
I am using gcc 4.6.3. However, I believe the bug is also in the latest headers
in the CVS (trunk).
A common use case for condition_variables, is something like this:
std::mutex mutex;
std::condition_variable_any cv;
// called by thread#1: waits for data from another thread
void wait_for_data()
{
std::unique_lock<std::mutex> lock(mutex);
cv.wait_for(lock, std::chrono::seconds(2)); // no predicate for simplicity
// dequeue data
}
// called by thread#2: passes data to waiting thread
void provide_data()
{
std::unique_lock<std::mutex> lock(mutex);
// enqueue data
cv.notify_one();
}
If thread#1's timeout expires while thread#2 already holds the lock on "mutex",
this will deadlock.
This is because condition_variable_any uses another internal mutex, which is
usually acquired after "mutex". However, if the timeout expires, the internal
mutex is acquired before "mutex".
By adding a nonsense "sleep_for", we can actually make a simple test program
always deadlocks (see attachment).
Notably, the same test program does not deadlock, if a
boost::condition_variable_any or a std::condition_variable is used instead of a
std::condition_variable_any.
