https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92731
Bug ID: 92731
Summary: Data race on exception object thrown from std::future
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rrrlasse at hotmail dot com
Target Milestone: ---
Created attachment 47397
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47397&action=edit
TSan output and .ii file
The source is compiled with:
g++ cpp.cpp -lpthread -fsanitize=thread -Wall -Wextra
After running for around 100 - 500 iteration in the for-loop of the main
thread, TSan reports a data race between the destructor of the exception object
and the strlen() loop.
If you omit the std::move(packaged_task) the warning disappears.
uname -a: Linux ubuntu 5.0.0-29-generic #31-Ubuntu SMP Thu Sep 12 13:05:32 UTC
2019 x86_64 x86_64 x86_64 GNU/Linux
g++ --version: g++ (Ubuntu 8.3.0-6ubuntu1) 8.3.0
Since you can apparently only add a single attachment, I've colledted the .ii
file and tsan report in a zip file.
Source code:
#include <iostream>
#include <optional>
#include <stdexcept>
#include <mutex>
#include <future>
#include <cstring>
std::condition_variable cv;
std::mutex mu;
std::function<void()> job;
bool has_job = false;
void looper() {
for (;;) {
std::unique_lock <std::mutex> ul(mu);
while (!has_job) {
cv.wait(ul);
}
has_job = false;
job();
}
}
// g++ cpp.cpp -lpthread -fsanitize=thread -Wall -Wextra
int main() {
std::thread t = std::thread(looper);
for (int c = 0; ; c++) {
try {
std::packaged_task<void()> packaged_task([]() { throw
std::runtime_error("aaaaaaaaaaaaaaaaa"); });
std::future<void> task_future =
packaged_task.get_future();
{
std::unique_lock<std::mutex> ul(mu);
job = [&]() {
#if 1
// tsan warning
std::packaged_task<void ()> tmp(std::move(packaged_task));
tmp();
#else
// no warning
packaged_task();
#endif
};
has_job = true;
cv.notify_one();
}
task_future.get();
}
catch (const std::runtime_error& e) {
for (int i = 0; i < 10; i++) {
[[maybe_unused]] int a = strlen(e.what());
}
}
}
}
