1 /*****************************************************************************
4 idle.c -- code for interruptible delays without sleep(3).
7 interruptible_idle() -- delay for some time, interruptible by signal.
10 Sometimes you need more than one time delay per program, so alarm(3)
11 won't cut it. This code illustrates time delays with select(2).
14 Eric S. Raymond <esr@thyrsus.com>, 1997. This source code example
15 is part of fetchmail and the Unix Cookbook, and are released under the
16 MIT license. Compile with -DMAIN to build the demonstrator.
18 ******************************************************************************/
25 #include <fetchmail.h> /* for ROOT_UID */
32 volatile int lastsig; /* last signal received */
34 #ifdef SLEEP_WITH_ALARM
36 * The function of this variable is to remove the window during which a
37 * SIGALRM can hose the code (ALARM is triggered *before* pause() is called).
38 * This is a bit of a kluge; the real right thing would use sigprocmask(),
39 * sigsuspend(). This workaround lets the interval timer trigger the first
40 * alarm after the required interval and will then generate alarms
41 * seconds until it is certain that the critical section (ie., the window)
44 static sig_atomic_t alarm_latch = FALSE;
46 void gotsigalrm(int sig)
48 signal(sig, gotsigalrm);
52 #endif /* SLEEP_WITH_ALARM */
55 /* Various EMX-specific definitions */
56 static int itimerflag;
58 void itimerthread(void* dummy)
60 if (outlevel >= O_VERBOSE)
62 GT_("fetchmail: thread sleeping for %d sec.\n"), poll_interval);
65 _sleep2(poll_interval*1000);
66 kill((getpid()), SIGALRM);
71 int interruptible_idle(int seconds)
72 /* time for a pause in the action; return TRUE if awakened by signal */
77 #ifdef SLEEP_WITH_ALARM /* not normally on */
79 * We can't use sleep(3) here because we need an alarm(3)
80 * equivalent in order to implement server nonresponse timeout.
81 * We'll just assume setitimer(2) is available since fetchmail
82 * has to have a BSDoid socket layer to work at all.
85 * This code stopped working under glibc-2, apparently due
86 * to the change in signal(2) semantics. (The siginterrupt
87 * line, added later, should fix this problem.) John Stracke
88 * <francis@netscape.com> wrote:
90 * The problem seems to be that, after hitting the interval
91 * timer while talking to the server, the process no longer
92 * responds to SIGALRM. I put in printf()s to see when it
93 * reached the pause() for the poll interval, and I checked
94 * the return from setitimer(), and everything seemed to be
95 * working fine, except that the pause() just ignored SIGALRM.
96 * I thought maybe the itimer wasn't being fired, so I hit
97 * it with a SIGALRM from the command line, and it ignored
98 * that, too. SIGUSR1 woke it up just fine, and it proceeded
99 * to repoll--but, when the dummy server didn't respond, it
100 * never timed out, and SIGALRM wouldn't make it.
102 * (continued below...)
105 struct itimerval ntimeout;
107 ntimeout.it_interval.tv_sec = 5; /* repeat alarm every 5 secs */
108 ntimeout.it_interval.tv_usec = 0;
109 ntimeout.it_value.tv_sec = seconds;
110 ntimeout.it_value.tv_usec = 0;
112 siginterrupt(SIGALRM, 1);
114 signal(SIGALRM, gotsigalrm); /* first trap signals */
115 setitimer(ITIMER_REAL,&ntimeout,NULL); /* then start timer */
116 /* there is a very small window between the next two lines */
117 /* which could result in a deadlock. But this will now be */
118 /* caught by periodic alarms (see it_interval) */
122 ntimeout.it_interval.tv_sec = ntimeout.it_interval.tv_usec = 0;
123 ntimeout.it_value.tv_sec = ntimeout.it_value.tv_usec = 0;
124 setitimer(ITIMER_REAL,&ntimeout,NULL); /* now stop timer */
125 signal(SIGALRM, SIG_IGN);
129 * So the workaround I used is to make it sleep by using
130 * select() instead of setitimer()/pause(). select() is
131 * perfectly happy being called with a timeout and
132 * no file descriptors; it just sleeps until it hits the
133 * timeout. The only concern I had was that it might
134 * implement its timeout with SIGALRM--there are some
135 * Unices where this is done, because select() is a library
136 * function--but apparently not.
139 struct timeval timeout;
141 timeout.tv_sec = seconds;
145 select(0,0,0,0, &timeout);
146 } while (lastsig == SIGCHLD);
151 signal(SIGALRM, gotsigalrm);
152 _beginthread(itimerthread, NULL, 32768, NULL);
153 /* see similar code above */
156 signal(SIGALRM, SIG_IGN);
158 if (lastsig == SIGUSR1 || ((seconds && getuid() == ROOT_UID)
159 && lastsig == SIGHUP))
162 /* now lock out interrupts again */
163 signal(SIGUSR1, SIG_IGN);
164 if (getuid() == ROOT_UID)
165 signal(SIGHUP, SIG_IGN);
167 return(awoken ? lastsig : 0);
171 int main(int argc, char **argv)
175 printf("How may I serve you, master?\n");
176 interruptible_idle(5);
181 /* idle.c ends here */