Date: Mon, 2 Oct 2017 08:34:26 +0200 From: Matthias Apitz <guru@unixarea.de> To: freebsd-questions@freebsd.org Subject: no dead-lock when signal handler calls localtime_r() on FreeBSD, but on Linux Message-ID: <20171002063425.GA21552@sh4-5.1blu.de>
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Hello,
I'm on the way clarifying a deadlock-issue we face on Linux when localtime_r()
is called in a signal-handler funtion. If you compile the code attached
below with gcc on Linux, the code gives what one deserves: a dead-lock
when Ctrl-C is pressed.
Interestingly this does not give a dead-lock on my FreeBSD (12-CURRENT)
system. I checked our man page sigaction(2) but the function is not in
the list of functions which may be called safe in signal-handlern.
Any idea, while this does not give a dead-lock on FreeBSD too?
Thanks
matthias
/*
* compile with: gcc -Wall -DUNSAFE -o deadlock deadlock.c
* to get a dead-lock
*
*/
#include <signal.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
void handler(int signum)
{
char result[100];
time_t now;
struct tm time1;
printf("in handler() now calling localtime_r() ...\n");
fflush(stdout);
now = time(NULL);
localtime_r(&now, &time1);
strftime(result, 100, "%T", &time1);
printf("... at %s, user pressed Ctrl-C\n", result);
}
int main (void)
{
time_t now;
struct tm ltime;
if (signal(SIGINT, handler) == SIG_IGN)
signal(SIGINT, SIG_IGN);
now = time(NULL);
while(1) {
#ifdef UNSAFE
localtime_r(&now, <ime);
#endif
}
return 0;
}
--
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