https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111726
Bug ID: 111726
Summary: Data race in std::poisson_distribution
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: rugasikrisztian at gmail dot com
Target Milestone: ---
The following program, which uses separate std::poisson_distribution instances
on multiple threads, has a data race in both the constructor and operator() of
the distribution:
https://godbolt.org/z/r1ojKdYna
#include <random>
#include <thread>
int rand_poisson() {
thread_local std::mt19937_64 gen{ 0x123456789 };
std::poisson_distribution<int> dist{ 15.0 };
return dist(gen);
}
int main() {
std::jthread T1{ rand_poisson };
std::jthread T2{ rand_poisson };
}
Compiled with gcc 13.2 and the options -std=c++20 -O3 -fsanitize=thread, the
output is:
==================
WARNING: ThreadSanitizer: data race (pid=1)
Write of size 4 at 0x7fed5e87a108 by thread T2:
#0 lgamma <null> (libtsan.so.2+0x536da) (BuildId:
dd14181575b14129bf3264ad0047089fc45e39d4)
#1 std::poisson_distribution<int>::param_type::_M_initialize()
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1275
(output.s+0x4014a0) (BuildId: 835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
#2 std::poisson_distribution<int>::param_type::param_type(double)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/random.h:4573
(output.s+0x4014a0)
#3 std::poisson_distribution<int>::poisson_distribution(double)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/random.h:4609
(output.s+0x4014a0)
#4 rand_poisson() /app/example.cpp:6 (output.s+0x4014a0)
#5 int std::__invoke_impl<int, int (*)()>(std::__invoke_other, int (*&&)())
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/invoke.h:61
(output.s+0x401559) (BuildId: 835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
#6 std::__invoke_result<int (*)()>::type std::__invoke<int (*)()>(int
(*&&)()) /opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/invoke.h:96
(output.s+0x401559)
#7 int std::thread::_Invoker<std::tuple<int (*)()>
>::_M_invoke<0ul>(std::_Index_tuple<0ul>)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:292
(output.s+0x401559)
#8 std::thread::_Invoker<std::tuple<int (*)()> >::operator()()
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:299
(output.s+0x401559)
#9 std::thread::_State_impl<std::thread::_Invoker<std::tuple<int (*)()> >
>::_M_run()
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:244
(output.s+0x401559)
#10 <null> <null> (libstdc++.so.6+0xe8ad2) (BuildId:
9f3caf39aab289429a6a218ddc8d4c9ff5ef08a4)
Previous write of size 4 at 0x7fed5e87a108 by thread T1:
#0 lgamma <null> (libtsan.so.2+0x536da) (BuildId:
dd14181575b14129bf3264ad0047089fc45e39d4)
#1 int
std::poisson_distribution<int>::operator()<std::mersenne_twister_engine<unsigned
long, 64ul, 312ul, 156ul, 31ul, 13043109905998158313ul, 29ul,
6148914691236517205ul, 17ul, 8202884508482404352ul, 37ul,
18444473444759240704ul, 43ul, 6364136223846793005ul>
>(std::mersenne_twister_engine<unsigned long, 64ul, 312ul, 156ul, 31ul,
13043109905998158313ul, 29ul, 6148914691236517205ul, 17ul,
8202884508482404352ul, 37ul, 18444473444759240704ul, 43ul,
6364136223846793005ul>&, std::poisson_distribution<int>::param_type const&)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1388
(output.s+0x40255c) (BuildId: 835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
#2 int
std::poisson_distribution<int>::operator()<std::mersenne_twister_engine<unsigned
long, 64ul, 312ul, 156ul, 31ul, 13043109905998158313ul, 29ul,
6148914691236517205ul, 17ul, 8202884508482404352ul, 37ul,
18444473444759240704ul, 43ul, 6364136223846793005ul>
>(std::mersenne_twister_engine<unsigned long, 64ul, 312ul, 156ul, 31ul,
13043109905998158313ul, 29ul, 6148914691236517205ul, 17ul,
8202884508482404352ul, 37ul, 18444473444759240704ul, 43ul,
6364136223846793005ul>&)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/random.h:4666
(output.s+0x401524) (BuildId: 835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
#3 rand_poisson() /app/example.cpp:7 (output.s+0x401524)
#4 int std::__invoke_impl<int, int (*)()>(std::__invoke_other, int (*&&)())
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/invoke.h:61
(output.s+0x401559) (BuildId: 835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
#5 std::__invoke_result<int (*)()>::type std::__invoke<int (*)()>(int
(*&&)()) /opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/invoke.h:96
(output.s+0x401559)
#6 int std::thread::_Invoker<std::tuple<int (*)()>
>::_M_invoke<0ul>(std::_Index_tuple<0ul>)
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:292
(output.s+0x401559)
#7 std::thread::_Invoker<std::tuple<int (*)()> >::operator()()
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:299
(output.s+0x401559)
#8 std::thread::_State_impl<std::thread::_Invoker<std::tuple<int (*)()> >
>::_M_run()
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/bits/std_thread.h:244
(output.s+0x401559)
#9 <null> <null> (libstdc++.so.6+0xe8ad2) (BuildId:
9f3caf39aab289429a6a218ddc8d4c9ff5ef08a4)
Location is global '__signgam' of size 4 at 0x7fed5e87a108
(libm.so.6+0x14e108)
Thread T2 (tid=4, running) created by main thread at:
#0 pthread_create <null> (libtsan.so.2+0x40cd6) (BuildId:
dd14181575b14129bf3264ad0047089fc45e39d4)
#1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State,
std::default_delete<std::thread::_State> >, void (*)()) <null>
(libstdc++.so.6+0xe8e4b) (BuildId: 9f3caf39aab289429a6a218ddc8d4c9ff5ef08a4)
#2 main /app/example.cpp:12 (output.s+0x40126a) (BuildId:
835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
Thread T1 (tid=3, finished) created by main thread at:
#0 pthread_create <null> (libtsan.so.2+0x40cd6) (BuildId:
dd14181575b14129bf3264ad0047089fc45e39d4)
#1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State,
std::default_delete<std::thread::_State> >, void (*)()) <null>
(libstdc++.so.6+0xe8e4b) (BuildId: 9f3caf39aab289429a6a218ddc8d4c9ff5ef08a4)
#2 main /app/example.cpp:11 (output.s+0x40125b) (BuildId:
835919b751a9e2f5ac4bdd461e8f650240b0a6eb)
SUMMARY: ThreadSanitizer: data race
(/opt/compiler-explorer/gcc-13.2.0/lib64/libtsan.so.2+0x536da) (BuildId:
dd14181575b14129bf3264ad0047089fc45e39d4) in lgamma
==================
ThreadSanitizer: reported 1 warnings
As far as I can tell this issue has been present since the initial
implementation of std::poisson_distribution.
The cause of it is that the implementation uses the lgamma function, which
modifies a global variable.
