Hi,
While developing a multi-threaded application I've encountered a problem that
is reproduced in a testcase presented below.
The purpose of the sample is to create a large number of threads where each
thread uses stl strings. The threads execute consecutively and not in parallel.
The problem is that the program crashes with a segmentation fault at line 14
(string instantiation in the f function) in thread number 4095 which is the
4097-th created thread (including the main thread). The segmentation fault
doesn't happen if line 23 is removed (assignment of a value into
std::map<string, string> in mt_test function). The problem is also reproduced
if the insertion into map is replaced with insertion into a
std::vector<std::string> or std::list<std::string>. I've found that
mt_allocator.h defines 4096 as the maximum number of threads in the freelist
(_S_max_threads enum) which seems to be related to the problem.
The source code:
#include <iostream>
#include <string>
#include <pthread.h>
#include <stdio.h>
#include <map>
#include <vector>
#include <list>
using namespace std;
void* f(void *arg)
{
int i = (int)arg;
string str = "foobar"; // <-- segmentation fault
cout << "finished:"<< i << endl;
return 0;
}
void mt_test()
{
string str1("f");
map<string, string> myMap;
myMap[str1] = "akjshd"; // <-- if removed, no crash
const int NUM_THREADS = 6000;
void* ret=0;
for(int i=0;i<NUM_THREADS;++i)
{
pthread_t thread;
int retVal = pthread_create(&thread, NULL, f, (void*)i);
if (retVal != 0)
{
cout << "error: " << retVal << endl;
exit(-1);
}
pthread_join(thread, &ret);
}
}
int main(int argc, char *argv[])
{
mt_test();
return EXIT_SUCCESS;
}
System info:
Compiler: GNU C++ version 4.0.0 20050519 (Red Hat 4.0.0-8) (i386-redhat-linux)
Creating the executable with:
$g++ -v -Wall -lpthread testthread.cpp -o testthread
Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,java,f95,ada --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre
--host=i386-redhat-linux
Thread model: posix
gcc version 4.0.0 20050519 (Red Hat 4.0.0-8)
/usr/libexec/gcc/i386-redhat-linux/4.0.0/cc1plus -quiet -v -D_GNU_SOURCE
../src/testthread.cpp -quiet -dumpbase testthread.cpp -auxbase testthread -Wall
-version -o /tmp/ccCvBzFs.s
ignoring nonexistent directory
"/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../../i386-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../../include/c++/4.0.0
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../../include/c++/4.0.0/i386-redhat-linux
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../../include/c++/4.0.0/backward
/usr/local/include
/usr/lib/gcc/i386-redhat-linux/4.0.0/include
/usr/include
End of search list.
GNU C++ version 4.0.0 20050519 (Red Hat 4.0.0-8) (i386-redhat-linux)
compiled by GNU C version 4.0.0 20050519 (Red Hat 4.0.0-8).
GGC heuristics: --param ggc-min-expand=99 --param ggc-min-heapsize=129317
as -V -Qy -o /tmp/ccSuAMBj.o /tmp/ccCvBzFs.s
GNU assembler version 2.15.94.0.2.2 (i386-redhat-linux) using BFD version
2.15.94.0.2.2 20041220
/usr/libexec/gcc/i386-redhat-linux/4.0.0/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o testthread
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../crt1.o
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../crti.o
/usr/lib/gcc/i386-redhat-linux/4.0.0/crtbegin.o
-L/usr/lib/gcc/i386-redhat-linux/4.0.0 -L/usr/lib/gcc/i386-redhat-linux/4.0.0
-L/usr/lib/gcc/i386-redhat-linux/4.0.0/../../.. -lpthread /tmp/ccSuAMBj.o
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/i386-redhat-linux/4.0.0/crtend.o
/usr/lib/gcc/i386-redhat-linux/4.0.0/../../../crtn.o
Libraries:
$ ldd testthread
linux-gate.so.1 => (0x0029e000)
libpthread.so.0 => /lib/libpthread.so.0 (0x0063b000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00795000)
libm.so.6 => /lib/libm.so.6 (0x00524000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00753000)
libc.so.6 => /lib/libc.so.6 (0x003f8000)
/lib/ld-linux.so.2 (0x003d6000)
Performing a backtrace with gdb gives:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1208943696 (LWP 32755)]
0x007d7977 in __gnu_cxx::__pool<true>::_M_get_thread_id () from
/usr/lib/libstdc++.so.6
(gdb) backtrace
#0 0x007d7977 in __gnu_cxx::__pool<true>::_M_get_thread_id () from
/usr/lib/libstdc++.so.6
#1 0x007d7e0c in __gnu_cxx::__pool<true>::_M_reclaim_block () from
/usr/lib/libstdc++.so.6
#2 0x0082227d in std::string::_Rep::_S_create () from /usr/lib/libstdc++.so.6
#3 0x0082625f in std::operator+<char, std::char_traits<char>,
std::allocator<char> > () from /usr/lib/libstdc++.so.6
#4 0x00826e7c in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string () from /usr/lib/libstdc++.so.6
#5 0x08049067 in f (arg=0xfff) at
/home/sveta-c/testthread/src/testthread.cpp:14
#6 0x00640b80 in start_thread () from /lib/libpthread.so.0
#7 0x004c2dee in clone () from /lib/libc.so.6
I would really appriciate any help on the subject.
Thanks in advance,
Sveta.
--
Summary: A problem with STL map/vector/list whose key is a STL
string in multi-threaded application
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sveta dot cher at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36270
