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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>
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commit 4a16d072723b48699ea162da24eff05eba298834 1 parent 479b0ae
Jeff King peff authored gitster committed
1  .gitignore
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@@ -152,6 +152,7 @@ test-match-trees
test-parse-options
test-path-utils
test-sha1
+test-sigchain
common-cmds.h
*.tar.gz
*.dsc
3  Makefile
View
@@ -388,6 +388,7 @@ LIB_H += revision.h
LIB_H += run-command.h
LIB_H += sha1-lookup.h
LIB_H += sideband.h
+LIB_H += sigchain.h
LIB_H += strbuf.h
LIB_H += tag.h
LIB_H += transport.h
@@ -481,6 +482,7 @@ LIB_OBJS += sha1-lookup.o
LIB_OBJS += sha1_name.o
LIB_OBJS += shallow.o
LIB_OBJS += sideband.o
+LIB_OBJS += sigchain.o
LIB_OBJS += strbuf.o
LIB_OBJS += symlinks.o
LIB_OBJS += tag.o
@@ -1364,6 +1366,7 @@ TEST_PROGRAMS += test-match-trees$X
TEST_PROGRAMS += test-parse-options$X
TEST_PROGRAMS += test-path-utils$X
TEST_PROGRAMS += test-sha1$X
+TEST_PROGRAMS += test-sigchain$X
all:: $(TEST_PROGRAMS)
5 builtin-clone.c
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@@ -19,6 +19,7 @@
#include "strbuf.h"
#include "dir.h"
#include "pack-refs.h"
+#include "sigchain.h"
/*
* Overall FIXMEs:
@@ -288,7 +289,7 @@ static void remove_junk(void)
static void remove_junk_on_signal(int signo)
{
remove_junk();
- signal(SIGINT, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -438,7 +439,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
}
junk_git_dir = git_dir;
atexit(remove_junk);
- signal(SIGINT, remove_junk_on_signal);
+ sigchain_push(SIGINT, remove_junk_on_signal);
setenv(CONFIG_ENVIRONMENT, xstrdup(mkpath("%s/config", git_dir)), 1);
5 builtin-fetch--tool.c
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@@ -2,6 +2,7 @@
#include "cache.h"
#include "refs.h"
#include "commit.h"
+#include "sigchain.h"
static char *get_stdin(void)
{
@@ -186,7 +187,7 @@ static void remove_keep(void)
static void remove_keep_on_signal(int signo)
{
remove_keep();
- signal(SIGINT, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -245,7 +246,7 @@ static int fetch_native_store(FILE *fp,
char buffer[1024];
int err = 0;
- signal(SIGINT, remove_keep_on_signal);
+ sigchain_push(SIGINT, remove_keep_on_signal);
atexit(remove_keep);
while (fgets(buffer, sizeof(buffer), stdin)) {
5 builtin-fetch.c
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@@ -10,6 +10,7 @@
#include "transport.h"
#include "run-command.h"
#include "parse-options.h"
+#include "sigchain.h"
static const char * const builtin_fetch_usage[] = {
"git fetch [options] [<repository> <refspec>...]",
@@ -58,7 +59,7 @@ static void unlock_pack(void)
static void unlock_pack_on_signal(int signo)
{
unlock_pack();
- signal(SIGINT, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -672,7 +673,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
ref_nr = j;
}
- signal(SIGINT, unlock_pack_on_signal);
+ sigchain_push(SIGINT, unlock_pack_on_signal);
atexit(unlock_pack);
exit_code = do_fetch(transport,
parse_fetch_refspec(ref_nr, refs), ref_nr);
5 diff.c
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@@ -12,6 +12,7 @@
#include "run-command.h"
#include "utf8.h"
#include "userdiff.h"
+#include "sigchain.h"
#ifdef NO_FAST_WORKING_DIRECTORY
#define FAST_WORKING_DIRECTORY 0
@@ -188,7 +189,7 @@ static void remove_tempfile(void)
static void remove_tempfile_on_signal(int signo)
{
remove_tempfile();
- signal(SIGINT, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -1902,7 +1903,7 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
if (!remove_tempfile_installed) {
atexit(remove_tempfile);
- signal(SIGINT, remove_tempfile_on_signal);
+ sigchain_push(SIGINT, remove_tempfile_on_signal);
remove_tempfile_installed = 1;
}
11 http-push.c
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@@ -10,6 +10,7 @@
#include "exec_cmd.h"
#include "remote.h"
#include "list-objects.h"
+#include "sigchain.h"
#include <expat.h>
@@ -1363,7 +1364,7 @@ static void remove_locks(void)
static void remove_locks_on_signal(int signo)
{
remove_locks();
- signal(signo, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -2261,10 +2262,10 @@ int main(int argc, char **argv)
goto cleanup;
}
- signal(SIGINT, remove_locks_on_signal);
- signal(SIGHUP, remove_locks_on_signal);
- signal(SIGQUIT, remove_locks_on_signal);
- signal(SIGTERM, remove_locks_on_signal);
+ sigchain_push(SIGINT, remove_locks_on_signal);
+ sigchain_push(SIGHUP, remove_locks_on_signal);
+ sigchain_push(SIGQUIT, remove_locks_on_signal);
+ sigchain_push(SIGTERM, remove_locks_on_signal);
/* Check whether the remote has server info files */
remote->can_update_info_refs = 0;
13 lockfile.c
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@@ -2,6 +2,7 @@
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
+#include "sigchain.h"
static struct lock_file *lock_file_list;
static const char *alternate_index_output;
@@ -24,7 +25,7 @@ static void remove_lock_file(void)
static void remove_lock_file_on_signal(int signo)
{
remove_lock_file();
- signal(signo, SIG_DFL);
+ sigchain_pop(signo);
raise(signo);
}
@@ -136,11 +137,11 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
if (0 <= lk->fd) {
if (!lock_file_list) {
- signal(SIGINT, remove_lock_file_on_signal);
- signal(SIGHUP, remove_lock_file_on_signal);
- signal(SIGTERM, remove_lock_file_on_signal);
- signal(SIGQUIT, remove_lock_file_on_signal);
- signal(SIGPIPE, remove_lock_file_on_signal);
+ sigchain_push(SIGINT, remove_lock_file_on_signal);
+ sigchain_push(SIGHUP, remove_lock_file_on_signal);
+ sigchain_push(SIGTERM, remove_lock_file_on_signal);
+ sigchain_push(SIGQUIT, remove_lock_file_on_signal);
+ sigchain_push(SIGPIPE, remove_lock_file_on_signal);
atexit(remove_lock_file);
}
lk->owner = getpid();
43 sigchain.c
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@@ -0,0 +1,43 @@
+#include "sigchain.h"
+#include "cache.h"
+
+#define SIGCHAIN_MAX_SIGNALS 32
+
+struct sigchain_signal {
+ sigchain_fun *old;
+ int n;
+ int alloc;
+};
+static struct sigchain_signal signals[SIGCHAIN_MAX_SIGNALS];
+
+static void check_signum(int sig)
+{
+ if (sig < 1 || sig >= SIGCHAIN_MAX_SIGNALS)
+ die("BUG: signal out of range: %d", sig);
+}
+
+int sigchain_push(int sig, sigchain_fun f)
+{
+ struct sigchain_signal *s = signals + sig;
+ check_signum(sig);
+
+ ALLOC_GROW(s->old, s->n + 1, s->alloc);
+ s->old[s->n] = signal(sig, f);
+ if (s->old[s->n] == SIG_ERR)
+ return -1;
+ s->n++;
+ return 0;
+}
+
+int sigchain_pop(int sig)
+{
+ struct sigchain_signal *s = signals + sig;
+ check_signum(sig);
+ if (s->n < 1)
+ return 0;
+
+ if (signal(sig, s->old[s->n - 1]) == SIG_ERR)
+ return -1;
+ s->n--;
+ return 0;
+}
9 sigchain.h
View
@@ -0,0 +1,9 @@
+#ifndef SIGCHAIN_H
+#define SIGCHAIN_H
+
+typedef void (*sigchain_fun)(int);
+
+int sigchain_push(int sig, sigchain_fun f);
+int sigchain_pop(int sig);
+
+#endif /* SIGCHAIN_H */
22 t/t0005-signals.sh
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@@ -0,0 +1,22 @@
+#!/bin/sh
+
+test_description='signals work as we expect'
+. ./test-lib.sh
+
+cat >expect <<EOF
+three
+two
+one
+EOF
+
+test_expect_success 'sigchain works' '
+ test-sigchain >actual
+ case "$?" in
+ 130) true ;; # POSIX w/ SIGINT=2
+ 3) true ;; # Windows
+ *) false ;;
+ esac &&
+ test_cmp expect actual
+'
+
+test_done
22 test-sigchain.c
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@@ -0,0 +1,22 @@
+#include "sigchain.h"
+#include "cache.h"
+
+#define X(f) \
+static void f(int sig) { \
+ puts(#f); \
+ fflush(stdout); \
+ sigchain_pop(sig); \
+ raise(sig); \
+}
+X(one)
+X(two)
+X(three)
+#undef X
+
+int main(int argc, char **argv) {
+ sigchain_push(SIGINT, one);
+ sigchain_push(SIGINT, two);
+ sigchain_push(SIGINT, three);
+ raise(SIGINT);
+ return 0;
+}
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