chain kill signals for cleanup functions
If a piece of code wanted to do some cleanup before exiting
(e.g., cleaning up a lockfile or a tempfile), our usual
strategy was to install a signal handler that did something
like this:
do_cleanup(); /* actual work */
signal(signo, SIG_DFL); /* restore previous behavior */
raise(signo); /* deliver signal, killing ourselves */
For a single handler, this works fine. However, if we want
to clean up two _different_ things, we run into a problem.
The most recently installed handler will run, but when it
removes itself as a handler, it doesn't put back the first
handler.
This patch introduces sigchain, a tiny library for handling
a stack of signal handlers. You sigchain_push each handler,
and use sigchain_pop to restore whoever was before you in
the stack.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2009-01-22 07:02:35 +01:00
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#include "sigchain.h"
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#include "cache.h"
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#define SIGCHAIN_MAX_SIGNALS 32
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struct sigchain_signal {
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sigchain_fun *old;
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int n;
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int alloc;
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};
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static struct sigchain_signal signals[SIGCHAIN_MAX_SIGNALS];
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static void check_signum(int sig)
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{
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if (sig < 1 || sig >= SIGCHAIN_MAX_SIGNALS)
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die("BUG: signal out of range: %d", sig);
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}
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int sigchain_push(int sig, sigchain_fun f)
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{
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struct sigchain_signal *s = signals + sig;
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check_signum(sig);
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ALLOC_GROW(s->old, s->n + 1, s->alloc);
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s->old[s->n] = signal(sig, f);
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if (s->old[s->n] == SIG_ERR)
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return -1;
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s->n++;
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return 0;
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}
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int sigchain_pop(int sig)
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{
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struct sigchain_signal *s = signals + sig;
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check_signum(sig);
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if (s->n < 1)
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return 0;
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if (signal(sig, s->old[s->n - 1]) == SIG_ERR)
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return -1;
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s->n--;
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return 0;
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}
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2009-01-22 07:03:08 +01:00
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void sigchain_push_common(sigchain_fun f)
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{
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sigchain_push(SIGINT, f);
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sigchain_push(SIGHUP, f);
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sigchain_push(SIGTERM, f);
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sigchain_push(SIGQUIT, f);
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sigchain_push(SIGPIPE, f);
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}
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