Handles the masked signal when the thread exits
Gibeom Gwon
gb.gwon@stackframe.dev
Thu Nov 18 18:25:29 GMT 2021
On 11/19/21 03:19, Florian Weimer wrote:
> * Gibeom Gwon:
>
>> On 11/19/21 03:08, Florian Weimer wrote:
>>> * Gibeom Gwon:
>>>
>>>> I am experiencing strange(unintended?) behavior when using pthread
>>>> with signals. If I set the signal mask with pthread_sigmask() in the
>>>> thread function and the process has pending signal when thread is
>>>> exiting, signal handler executed in thread.
>>>>
>>>> It looks like glibc restores original signal mask at the end of the
>>>> thread. So I suspect this eventually triggers masked signal
>>>> handler. But I'm not sure it is intended or not.
>>> Which glibc version are you using?
>
>> Ah, I forgot to write the version. I'm using 2.33 and linux
>> distribution is Arch Linux.
>
> We had some issues with signals and thread exit in 2.34, but they are
> exclusive to that release and cannot happen in 2.33. I can't reproduce
> the behavior you see with upstream 2.33, either.
>
> What's your kernel version? I've tried 5.14.13 and 5.14.17.
>
> Thanks,
> Florian
>
Kernel version is 5.15.2.
Well, I accidently dropped sleep.c code sample. Here are the code
samples again. Sorry to bother you.
sleep.c
-------
#include <unistd.h>
int main() {
sleep(50);
return 0;
}
signal.c
--------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <pthread.h>
pthread_t thread;
pid_t pid;
void stop_threads() {
pthread_cancel(thread);
pthread_join(thread, NULL);
}
void sigint_handler(int signum) {
printf("sigint: %ld\n",pthread_self());
stop_threads();
exit(0);
}
void sigchld_handler(int signum) {
printf("sigchld: %ld\n",pthread_self());
pid_t pid;
int status;
while((pid = waitpid(-1,&status,WNOHANG)) > 0) {}
}
void spawn_sleep() {
pid = fork();
if(pid == 0)
execl("./sleep","sleep",NULL);
}
void* worker(void *arg) {
sigset_t mask;
sigfillset(&mask);
pthread_sigmask(SIG_SETMASK,&mask,NULL);
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE,NULL);
int i = 10;
while(i) {
printf("worker...\n");
sleep(1);
i--;
}
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE,NULL);
printf("thread close\n");
pthread_exit(0);
}
void spawn_thread() {
pthread_create(&thread,NULL,worker,NULL);
printf("child thread: %ld\n",thread);
}
int main() {
printf("main thread: %ld\n",pthread_self());
spawn_sleep();
struct sigaction sa1;
sa1.sa_handler = sigint_handler;
sigemptyset(&sa1.sa_mask);
sigaddset(&sa1.sa_mask,SIGCHLD);
sa1.sa_flags = 0;
sigaction(SIGINT, &sa1, 0);
struct sigaction sa2;
sa2.sa_handler = sigchld_handler;
sigemptyset(&sa2.sa_mask);
sa2.sa_flags = 0;
sigaction(SIGCHLD, &sa2, 0);
spawn_thread();
while(1)
sleep(1);
return 0;
}
Regards,
Gibeom Gwon
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