On Tue, Apr 6, 2010 at 2:17 PM, Bart Van Assche <[email protected]> wrote:
> On Tue, Apr 6, 2010 at 7:53 AM, Jorge Moraleda <[email protected]>
> wrote:
> >
> > Dear all,
> >
> > When I compile the following program with:
> > $ g++ -g -pthread threads.cpp
> >
> > // begin program /////////////////////////////////////////////
> > // file: threads.cpp
> > #include <pthread.h>
> > #include <iostream>
> > #include <sstream>
> >
> > void *threadEntry(void *threadid)
> > {
> > long tid;
> > tid = (long)threadid;
> > for (int i = 0; i<5; i++) {
> > std::stringstream myStream;
> > myStream << "this thread is " << tid;
> > std::string myString(myStream.str());
> > pthread_yield();
> > }
> > pthread_exit(NULL);
> > }
> >
> > int main (int argc, char *argv[])
> > {
> > pthread_t threads[2];
> > int rc;
> > long t;
> > for(t=0; t<2; t++) {
> > rc = pthread_create(&threads[t], NULL, threadEntry, (void *)t);
> > }
> > pthread_exit(NULL);
> > }
> > // end program /////////////////////////////////////////////
> >
> > and run drd on it with:
> > $ valgrind --tool=drd ./a.out
> >
> > I get the following output:
> >
> > ==16240== drd, a thread error detector
> > ==16240== Copyright (C) 2006-2009, and GNU GPL'd, by Bart Van Assche.
> > ==16240== Using Valgrind-3.5.0-Debian and LibVEX; rerun with -h for
> > copyright info
> > ==16240== Command: ./a.out
> > ==16240==
> > ==16240== Thread 3:
> > ==16240== Conflicting load by thread 3 at 0x05132e98 size 1
> > ==16240== at 0x4ED44C8: std::ostream&
> > std::ostream::_M_insert<long>(long) (in /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x400C48: threadEntry(void*) (threads.cpp:12)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240== Allocation context: BSS section of /usr/lib/libstdc++.so.6.0.13
> > ==16240== Other segment start (thread 2)
> > ==16240== at 0x4C29F2F: pthread_mutex_unlock
> (drd_pthread_intercepts.c:633)
> > ==16240== by 0x4EA387E: std::locale::locale() (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4E9FE5F: std::ios_base::_M_init() (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4EB4768: std::basic_ios<char, std::char_traits<char>
> > >::init(std::basic_streambuf<char, std::char_traits<char> >*) (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4ED7DEA: std::basic_stringstream<char,
> > std::char_traits<char>, std::allocator<char>
> > >::basic_stringstream(std::_Ios_Openmode) (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x400C21: threadEntry(void*) (threads.cpp:11)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240== Other segment end (thread 2)
> > ==16240== at 0x58ACEB7: sched_yield (in /lib/libc-2.10.1.so)
> > ==16240== by 0x400C63: threadEntry(void*) (threads.cpp:14)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240==
> > ==16240== Conflicting load by thread 3 at 0x05132eb9 size 1
> > ==16240== at 0x4ED44D3: std::ostream&
> > std::ostream::_M_insert<long>(long) (in /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x400C48: threadEntry(void*) (threads.cpp:12)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240== Allocation context: BSS section of /usr/lib/libstdc++.so.6.0.13
> > ==16240== Other segment start (thread 2)
> > ==16240== at 0x4C29F2F: pthread_mutex_unlock
> (drd_pthread_intercepts.c:633)
> > ==16240== by 0x4EA387E: std::locale::locale() (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4E9FE5F: std::ios_base::_M_init() (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4EB4768: std::basic_ios<char, std::char_traits<char>
> > >::init(std::basic_streambuf<char, std::char_traits<char> >*) (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x4ED7DEA: std::basic_stringstream<char,
> > std::char_traits<char>, std::allocator<char>
> > >::basic_stringstream(std::_Ios_Openmode) (in
> > /usr/lib/libstdc++.so.6.0.13)
> > ==16240== by 0x400C21: threadEntry(void*) (threads.cpp:11)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240== Other segment end (thread 2)
> > ==16240== at 0x58ACEB7: sched_yield (in /lib/libc-2.10.1.so)
> > ==16240== by 0x400C63: threadEntry(void*) (threads.cpp:14)
> > ==16240== by 0x4C32870: vgDrd_thread_wrapper
> (drd_pthread_intercepts.c:272)
> > ==16240== by 0x55E8A03: start_thread (pthread_create.c:300)
> > ==16240== by 0x58DD80C: clone (clone.S:112)
> > ==16240==
> > ==16240==
> > ==16240== For counts of detected and suppressed errors, rerun with: -v
> > ==16240== ERROR SUMMARY: 6 errors from 2 contexts (suppressed: 208 from
> 140)
> >
> > My question is: Are the errors reported real multi threading errors?
> > If not, how can I tell drd to suppress them? (In my real world program, I
> > have thousands of errors in hundreds of contexts, and I am trying to
> > find the real ones.)
> > If yes, can you help me understand what is wrong? Both threads only
> > use local variables. I have been reading about the global object
> > "locale" used by streams for localization, but I have read that it is
> > protected by a global mutex.
>
> Hello Jorge,
>
> Unfortunately not all libraries have been designed with data-race
> detection tools in mind. Several libraries contain code that triggers
> benign data races. Examples are the I/O code in libstdc++ and in libc.
>
> You can either create a suppression pattern to suppress the above
> races, or even simpler, add the following code in main() before thread
> creation starts:
>
> std::ostringstream dummy;
> dummy << 0;
>
> The above code will make sure that locale initialization, which is
> triggered by sending an number to an I/O stream, will happen before
> any threads are created and hence no races will be reported anymore on
> locale initialization.
>
This will not hide the race on _ZNSs4_Rep20_S_empty_rep_storageE.
And suppressing errors in string guts may hide real races.
>
> Bart.
>
>
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Try the new software tools for yourself. Speed compiling, find bugs
proactively, and fine-tune applications for parallel performance.
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