This is part of a test for thread safety. I'm running an anonymous lambda in different threads.
I use the variable i
as thread id.
Originally I passed every variable from main
scope by using [&]
, but this corrupts the heap.
Solved it now by passing i
by value, but for the life of me I can't figure out why this would cause problems on the heap since the threads are only reading i
.
Can anyone explain?
Minimal compilable example producing error:
#include <thread>
#include <vector>
using namespace std;
int main(int argc, char** argv) {
vector<thread> threads;
vector<string> vec1;
vector<string> vec2;
for (int i = 0; i < 2; i++) {
threads.push_back(
thread([&vec1, &vec2, &i]() {
for (int j = 0; j < 10; j++) {
const string str = "foo";
if (i == 0) {
vec1.push_back(str);
} else {
vec2.push_back(str);
}
}
})
);
}
for (auto& thread : threads) {
thread.join();
}
return 0;
}
Output:
*** Error in `/vagrant/bin/TempFileTest': double free or corruption (fasttop): 0x00007f00240008c0 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7f002a0e97e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7f002a0f237a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f002a0f653c]
/vagrant/bin/TempFileTest(_ZNSt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS5_EE19_M_emplace_back_auxIJRKS5_EEEvDpOT_+0x1a3)[0x4021b3]
/vagrant/bin/TempFileTest[0x401e83]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xb8c80)[0x7f002a70ac80]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x76ba)[0x7f002a9db6ba]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f002a17941d]
======= Memory map: ========
00400000-00403000 r-xp 00000000 08:02 2622834 /vagrant/bin/TempFileTest
00602000-00603000 r--p 00002000 08:02 2622834 /vagrant/bin/TempFileTest
00603000-00604000 rw-p 00003000 08:02 2622834 /vagrant/bin/TempFileTest
02182000-021b4000 rw-p 00000000 00:00 0 [heap]
7f001c000000-7f001c021000 rw-p 00000000 00:00 0
7f001c021000-7f0020000000 ---p 00000000 00:00 0
7f0024000000-7f0024021000 rw-p 00000000 00:00 0
7f0024021000-7f0028000000 ---p 00000000 00:00 0
7f0028d67000-7f0028d68000 ---p 00000000 00:00 0
7f0028d68000-7f0029568000 rw-p 00000000 00:00 0
7f0029568000-7f0029569000 ---p 00000000 00:00 0
7f0029569000-7f0029d69000 rw-p 00000000 00:00 0
7f0029d69000-7f0029e71000 r-xp 00000000 00:32 313 /lib/x86_64-linux-gnu/libm-2.23.so
7f0029e71000-7f002a070000 ---p 00108000 00:32 313 /lib/x86_64-linux-gnu/libm-2.23.so
7f002a070000-7f002a071000 r--p 00107000 00:32 313 /lib/x86_64-linux-gnu/libm-2.23.so
7f002a071000-7f002a072000 rw-p 00108000 00:32 313 /lib/x86_64-linux-gnu/libm-2.23.so
7f002a072000-7f002a232000 r-xp 00000000 00:32 45 /lib/x86_64-linux-gnu/libc-2.23.so
7f002a232000-7f002a432000 ---p 001c0000 00:32 45 /lib/x86_64-linux-gnu/libc-2.23.so
7f002a432000-7f002a436000 r--p 001c0000 00:32 45 /lib/x86_64-linux-gnu/libc-2.23.so
7f002a436000-7f002a438000 rw-p 001c4000 00:32 45 /lib/x86_64-linux-gnu/libc-2.23.so
7f002a438000-7f002a43c000 rw-p 00000000 00:00 0
7f002a43c000-7f002a452000 r-xp 00000000 00:32 314 /lib/x86_64-linux-gnu/libgcc_s.so.1
7f002a452000-7f002a651000 ---p 00016000 00:32 314 /lib/x86_64-linux-gnu/libgcc_s.so.1
7f002a651000-7f002a652000 rw-p 00015000 00:32 314 /lib/x86_64-linux-gnu/libgcc_s.so.1
7f002a652000-7f002a7c4000 r-xp 00000000 00:32 311 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f002a7c4000-7f002a9c4000 ---p 00172000 00:32 311 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f002a9c4000-7f002a9ce000 r--p 00172000 00:32 311 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f002a9ce000-7f002a9d0000 rw-p 0017c000 00:32 311 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f002a9d0000-7f002a9d4000 rw-p 00000000 00:00 0
7f002a9d4000-7f002a9ec000 r-xp 00000000 00:32 61 /lib/x86_64-linux-gnu/libpthread-2.23.so
7f002a9ec000-7f002abeb000 ---p 00018000 00:32 61 /lib/x86_64-linux-gnu/libpthread-2.23.so
7f002abeb000-7f002abec000 r--p 00017000 00:32 61 /lib/x86_64-linux-gnu/libpthread-2.23.so
7f002abec000-7f002abed000 rw-p 00018000 00:32 61 /lib/x86_64-linux-gnu/libpthread-2.23.so
7f002abed000-7f002abf1000 rw-p 00000000 00:00 0
7f002abf1000-7f002ac17000 r-xp 00000000 00:32 42 /lib/x86_64-linux-gnu/ld-2.23.so
7f002adf6000-7f002adfc000 rw-p 00000000 00:00 0
7f002ae15000-7f002ae16000 rw-p 00000000 00:00 0
7f002ae16000-7f002ae17000 r--p 00025000 00:32 42 /lib/x86_64-linux-gnu/ld-2.23.so
7f002ae17000-7f002ae18000 rw-p 00026000 00:32 42 /lib/x86_64-linux-gnu/ld-2.23.so
7f002ae18000-7f002ae19000 rw-p 00000000 00:00 0
7fff30694000-7fff306b5000 rw-p 00000000 00:00 0 [stack]
7fff30761000-7fff30763000 r--p 00000000 00:00 0 [vvar]
7fff30763000-7fff30765000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Aborted (core dumped)
Minimal compilable example without error (notice no &
on i
):
#include <thread>
#include <vector>
using namespace std;
int main(int argc, char** argv) {
vector<thread> threads;
vector<string> vec1;
vector<string> vec2;
for (int i = 0; i < 2; i++) {
threads.push_back(
thread([&vec1, &vec2, i]() {
for (int j = 0; j < 10; j++) {
const string str = "foo";
if (i == 0) {
vec1.push_back(str);
} else {
vec2.push_back(str);
}
}
})
);
}
for (auto& thread : threads) {
thread.join();
}
return 0;
}
I'm using:
Ubuntu 16.04
gcc 5.4.0
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