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>

diff --git a/.gitignore b/.gitignore
index d9adce585af99e617a2906a89029a92045a79538..f28a54d262e77f9bd457cd26f83dd78632fc3633 100644 (file)
--- a/.gitignore
+++ b/.gitignore
@@ -152,6 +152,7 @@ test-match-trees
 test-parse-options
 test-path-utils
 test-sha1
+test-sigchain
 common-cmds.h
 *.tar.gz
 *.dsc

diff --git a/Makefile b/Makefile
index 2b873fa99f8ddc70c7560fd64a516a051afc3a7a..fd02decc01a053ad31fdaac66fde86033c0f2bfb 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -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)
 

diff --git a/builtin-clone.c b/builtin-clone.c
index f1a1a0c36591d1936088a180e3c0a8ca5e7b0757..18b9392334a0931076855b175ab368deea8ac122 100644 (file)
--- a/builtin-clone.c
+++ b/builtin-clone.c
@@ -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);
 

diff --git a/builtin-fetch--tool.c b/builtin-fetch--tool.c
index 469b07e240953aa21fd67eb2563e094a7f0f3d42..b1d7f8fb32fd2d2ee6cfd18ed310a5d70e9e5ceb 100644 (file)
--- a/builtin-fetch--tool.c
+++ b/builtin-fetch--tool.c
@@ -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)) {

diff --git a/builtin-fetch.c b/builtin-fetch.c
index de6f3074b1121fdbcbe8bf0593dee446a17fb08e..8c86974cbee0341d7c0e110055bb4347ad5908ad 100644 (file)
--- a/builtin-fetch.c
+++ b/builtin-fetch.c
@@ -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);

diff --git a/diff.c b/diff.c
index 3cfc0b636c83d5012a138131db964c198a1a6c33..9c9977d892e475b0fa98a946393118ef59d73100 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -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;
        }
 

diff --git a/http-push.c b/http-push.c
index a4b7d08663504a57008f66a39fffe293f62c1d08..dec395deed0778b707b62e86a35086f6e6b73a72 100644 (file)
--- a/http-push.c
+++ b/http-push.c
@@ -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;

diff --git a/lockfile.c b/lockfile.c
index 8589155532da9eb7f42a1e9c3132fcf42b1b9275..3cd57dc3854c22b071619e03c3ccd26981b0c45b 100644 (file)
--- a/lockfile.c
+++ b/lockfile.c
@@ -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();

diff --git a/sigchain.c b/sigchain.c
new file mode 100644 (file)
index 0000000..a18d505
--- /dev/null
+++ b/sigchain.c
@@ -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;
+}

diff --git a/sigchain.h b/sigchain.h
new file mode 100644 (file)
index 0000000..254ebb0
--- /dev/null
+++ b/sigchain.h
@@ -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 */

diff --git a/t/t0005-signals.sh b/t/t0005-signals.sh
new file mode 100755 (executable)
index 0000000..9707af7
--- /dev/null
+++ b/t/t0005-signals.sh
@@ -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

diff --git a/test-sigchain.c b/test-sigchain.c
new file mode 100644 (file)
index 0000000..8747dea
--- /dev/null
+++ b/test-sigchain.c
@@ -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;
+}