Re: [Boost-users] thread lock-guard race condition

Subject: Re: [Boost-users] thread lock-guard race condition
From: Boost lzw (boostlzw_at_[hidden])
Date: 2010-11-24 22:48:52

Hi, Phil,

Valgrind user manual give no more information than " Applications that use
the Boost.Thread library should run fine under DRD." I ran your code using
DRD tool  of valgrind and got race warnings too.

I then ran the following thread_group.cpp code distributed with boost_1_42,
debugged it with valgrind --tool=drd, and it gave race warnings (more errors
than your code) too:

int count = 0;
boost::mutex mutex;

void increment_count()
{
    boost::mutex::scoped_lock lock(mutex);
    std::cout << "count = " << ++count << std::endl;
}

int main(int argc, char* argv[])
{
    boost::thread_group threads;
    for (int i = 0; i < 10; ++i)
        threads.create_thread(&increment_count);
    threads.join_all();
}

This suggests that valgrind might give false race warnings for boost thread
code. Although I am not 100% sure of it. BTW, what other debugging tools are
available to us for debugging boost threaded code?

Robert

On Wed, Nov 24, 2010 at 11:05 AM, Kraus Philipp
<philipp.kraus_at_[hidden]>wrote:

> Hello,
>
> I have written this little example:
>
> boost::mutex mutex;
>
> void thread()
> {
>     for (int i = 0; i < 5; ++i)
>     {
>         boost::this_thread::sleep(boost::posix_time::seconds(3));
>         boost::lock_guard<boost::mutex> lock(mutex);
>         std::cout << "Thread " << boost::this_thread::get_id() << ": " <<
> i << std::endl;
>     }
> }
>
> int main(int argc, char *argv[]) {
>     boost::thread t1(thread);
>     boost::thread t2(thread);
>     t1.join();
>     t2.join();
> }
>
> I compile the code with pthread option on the gcc (4.0.1). In the first
> case the program works, but if I use the helgrind tool of valgrind I'll get
> this errors (sorry for the long messages).
> I would like to understand what I have done wrong. I hope I understand the
> lock_guard in the correct way: If I create the lock with the mutex variable
> the thread, that creates the lock runs down the next lines. All other
> threads that run into the lock_guard line blocks until the lock variable of
> the first thread call the destructor (which should be on every loop
> iteration).
>
> Thanks for help
>
> Phil
>
>
> ------Valgrind Logs-----------
>
>
> ==19846== Thread #1 is the program's root thread
>
> ==19846== Thread #3 & #2 was created
> ==19846==    at 0x15A1FDE: __bsdthread_create (in
> /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x378F4: pthread_create_WRK (hg_intercepts.c:257)
> ==19846==    by 0x379C8: pthread_create (hg_intercepts.c:294)
> ==19846==    by 0x55C06: boost::thread::start_thread() (in
> libboost_thread.dylib)
> ==19846==    by 0x9FED: boost::thread::thread<void (*)()>(void (*)(),
> boost::disable_if<boost::is_convertible<void (*&)(),
> boost::detail::thread_move_t<void (*)()> >, boost::thread::dummy*>::type)
> (in ./main)
> ==19846==    by 0x2A82: main (in ./main)
>
> This message is show for thread #1, #2 and #3
>
> ==19846== Possible data race during read of size 4 at 0x5e008 by thread #3
> ==19846==    at 0x56381: void boost::call_once<void
> (*)()>(boost::once_flag&, void (*)()) (in libboost_thread.dylib)
> ==19846==    by 0x545AC: thread_proxy (in libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15A2011: thread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==  This conflicts with a previous write of size 4 by thread #2
> ==19846==    at 0x5647F: void boost::call_once<void
> (*)()>(boost::once_flag&, void (*)()) (in /libboost_thread.dylib)
> ==19846==    by 0x545AC: thread_proxy (in /libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15A2011: thread_start (in /usr/lib/libSystem.B.dylib)
>
> ==19846== Thread #2: Bug in libpthread: recursive write lock granted on
> mutex/wrlock which does not support recursion
> ==19846==    at 0x385D2: pthread_cond_timedwait_WRK (hg_intercepts.c:764)
> ==19846==    by 0x386B0: pthread_cond_timedwait$* (hg_intercepts.c:798)
> ==19846==    by 0x5AABB:
> boost::condition_variable::timed_wait(boost::unique_lock<boost::mutex>&,
> boost::posix_time::ptime const&) (in libboost_thread.dylib)
> ==19846==    by 0x54DC5: boost::this_thread::sleep(boost::posix_time::ptime
> const&) (in libboost_thread.dylib)
> ==19846==    by 0xEE31: void
> boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds
> const&) (in ./main)
> ==19846==    by 0x23F8: thread() (in ./main)
> ==19846==    by 0x545CC: thread_proxy (in libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15A2011: thread_start (in /usr/lib/libSystem.B.dylib)
>
> The next message is shown for the thread #2 & #3
>
> ==19846== Thread #3: lock order "0x2500668 before 0x25005C8" violated
> ==19846==    at 0x37E1B: pthread_mutex_lock (hg_intercepts.c:496)
> ==19846==    by 0x5ABA3:
> boost::condition_variable::timed_wait(boost::unique_lock<boost::mutex>&,
> boost::posix_time::ptime const&) (in libboost_thread.dylib)
> ==19846==    by 0x54DC5: boost::this_thread::sleep(boost::posix_time::ptime
> const&) (in libboost_thread.dylib)
> ==19846==    by 0xEE31: void
> boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds
> const&) (in ./main)
> ==19846==    by 0x23F8: thread() (in ./main)
> ==19846==    by 0x545CC: thread_proxy (in libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15A2011: thread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==   Required order was established by acquisition of lock at
> 0x2500668
> ==19846==    at 0x37E1B: pthread_mutex_lock (hg_intercepts.c:496)
> ==19846==    by 0x15A3452: _pthread_cond_wait (in
> /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15C89F7: pthread_cond_timedwait$UNIX2003 (in
> /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x38575: pthread_cond_timedwait_WRK (hg_intercepts.c:760)
> ==19846==    by 0x386B0: pthread_cond_timedwait$* (hg_intercepts.c:798)
> ==19846==    by 0x5AABB:
> boost::condition_variable::timed_wait(boost::unique_lock<boost::mutex>&,
> boost::posix_time::ptime const&) (in libboost_thread.dylib)
> ==19846==    by 0x54DC5: boost::this_thread::sleep(boost::posix_time::ptime
> const&) (in libboost_thread.dylib)
> ==19846==    by 0xEE31: void
> boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds
> const&) (in ./main)
> ==19846==    by 0x23F8: thread() (in ./main)
> ==19846==    by 0x545CC: thread_proxy (in libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==   followed by a later acquisition of lock at 0x25005C8
> ==19846==    at 0x37E1B: pthread_mutex_lock (hg_intercepts.c:496)
> ==19846==    by 0x53E6A: boost::this_thread::interruption_point() (in
> libboost_thread.dylib)
> ==19846==    by 0x5AAC2:
> boost::condition_variable::timed_wait(boost::unique_lock<boost::mutex>&,
> boost::posix_time::ptime const&) (in /libboost_thread.dylib)
> ==19846==    by 0x54DC5: boost::this_thread::sleep(boost::posix_time::ptime
> const&) (in libboost_thread.dylib)
> ==19846==    by 0xEE31: void
> boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds
> const&) (in ./main)
> ==19846==    by 0x23F8: thread() (in ./main)
> ==19846==    by 0x545CC: thread_proxy (in libboost_thread.dylib)
> ==19846==    by 0x37828: mythread_wrapper (hg_intercepts.c:221)
> ==19846==    by 0x15A2154: _pthread_start (in /usr/lib/libSystem.B.dylib)
> ==19846==    by 0x15A2011: thread_start (in /usr/lib/libSystem.B.dylib)
>
>
>
>
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