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cli: handle POSIX signals in a dedicated thread

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For a multihreaded application the safest way to handle unix signals is using
a dedicated thread that processes the signals by sigwait() function. All other
threads have these signals (processed by the thread) blocked.

A few useful links:
http://pubs.opengroup.org/onlinepubs/007904975/functions/sigwait.html
http://pic.dhe.ibm.com/infocenter/aix/v6r1/index.jsp?topic=%2Fcom.ibm.aix.genprogc%2Fdoc%2Fgenprogc%2Fsignal_mgmt.htm
http://www.linuxjournal.com/article/2121?page=0,2
http://www.redwoodsoft.com/~dru/unixbook/book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch12lev1sec8.html
https://www.securecoding.cert.org/confluence/display/seccode/CON37-C.+Do+not+call+signal%28%29+in+a+multithreaded+program
This commit is contained in:
Jiří Klimeš
2013-09-09 18:18:48 +02:00
parent ffa012f3ce
commit 663014ed62
1 changed files with 61 additions and 16 deletions
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77
cli/src/nmcli.c
View File

@@ -26,6 +26,7 @@
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <pthread.h>
#include <locale.h>
#include <glib.h>
@@ -55,6 +56,7 @@ typedef struct {
/* --- Global variables --- */
GMainLoop *loop = NULL;
static sigset_t signal_set;
/* Get an error quark for use with GError */
@@ -263,27 +265,67 @@ parse_command_line (NmCli *nmc, int argc, char **argv)
return nmc->return_value;
}
static void
signal_handler (int signo)
{
if (signo == SIGINT || signo == SIGTERM) {
g_message (_("Caught signal %d, shutting down..."), signo);
g_main_loop_quit (loop);
void *signal_handling_thread (void *arg);
/*
* Thread function waiting for signals and processing them.
* Wait for signals in signal set. The semantics of sigwait() require that all
* threads (including the thread calling sigwait()) have the signal masked, for
* reliable operation. Otherwise, a signal that arrives while this thread is
* not blocked in sigwait() might be delivered to another thread.
*/
void *
signal_handling_thread (void *arg) {
int signo;
while (1) {
sigwait (&signal_set, &signo);
switch (signo) {
case SIGINT:
case SIGQUIT:
case SIGTERM:
printf (_("\nError: nmcli terminated by signal %d."), signo);
exit (1);
break;
default:
break;
}
}
return NULL;
}
static void
/*
* Mask the signals we are interested in and create a signal handling thread.
* Because all threads inherit the signal mask from their creator, all threads
* in the process will have the signals masked. That's why setup_signals() has
* to be called before creating other threads.
*/
static gboolean
setup_signals (void)
{
struct sigaction action;
sigset_t mask;
pthread_t signal_thread_id;
int status;
sigemptyset (&mask);
action.sa_handler = signal_handler;
action.sa_mask = mask;
action.sa_flags = 0;
sigaction (SIGTERM, &action, NULL);
sigaction (SIGINT, &action, NULL);
sigemptyset (&signal_set);
sigaddset (&signal_set, SIGINT);
sigaddset (&signal_set, SIGQUIT);
sigaddset (&signal_set, SIGTERM);
/* Block all signals of interest. */
status = pthread_sigmask (SIG_BLOCK, &signal_set, NULL);
if (status != 0) {
fprintf (stderr, _("Failed to set signal mask: %d"), status);
return FALSE;
}
/* Create the signal handling thread. */
status = pthread_create (&signal_thread_id, NULL, signal_handling_thread, NULL);
if (status != 0) {
fprintf (stderr, _("Failed to create signal handling thread: %d"), status);
return FALSE;
}
return TRUE;
}
static NMClient *
@@ -368,6 +410,10 @@ main (int argc, char *argv[])
NmCli nmc;
ArgsInfo args_info = { &nmc, argc, argv };
/* Set up unix signal handling */
if (!setup_signals ())
exit (NMC_RESULT_ERROR_UNKNOWN);
/* Set locale to use environment variables */
setlocale (LC_ALL, "");
@@ -384,7 +430,6 @@ main (int argc, char *argv[])
g_idle_add (start, &args_info);
loop = g_main_loop_new (NULL, FALSE); /* create main loop */
setup_signals (); /* setup UNIX signals */
g_main_loop_run (loop); /* run main loop */
/* Print result descripting text */