From 4a16d072723b48699ea162da24eff05eba298834 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 22 Jan 2009 01:02:35 -0500 Subject: [PATCH] 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 Signed-off-by: Junio C Hamano --- .gitignore | 1 + Makefile | 3 +++ builtin-clone.c | 5 +++-- builtin-fetch--tool.c | 5 +++-- builtin-fetch.c | 5 +++-- diff.c | 5 +++-- http-push.c | 11 ++++++----- lockfile.c | 13 +++++++------ sigchain.c | 43 +++++++++++++++++++++++++++++++++++++++++++ sigchain.h | 9 +++++++++ t/t0005-signals.sh | 22 ++++++++++++++++++++++ test-sigchain.c | 22 ++++++++++++++++++++++ 12 files changed, 125 insertions(+), 19 deletions(-) create mode 100644 sigchain.c create mode 100644 sigchain.h create mode 100755 t/t0005-signals.sh create mode 100644 test-sigchain.c diff --git a/.gitignore b/.gitignore index d9adce585..f28a54d26 100644 --- 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 2b873fa99..fd02decc0 100644 --- 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 f1a1a0c36..18b939233 100644 --- 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 469b07e24..b1d7f8fb3 100644 --- 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 de6f3074b..8c86974cb 100644 --- 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] [ ...]", @@ -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 3cfc0b636..9c9977d89 100644 --- 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 a4b7d0866..dec395dee 100644 --- 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 @@ -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 858915553..3cd57dc38 100644 --- 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 index 000000000..a18d505e5 --- /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 index 000000000..254ebb0fa --- /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 index 000000000..9707af7d0 --- /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 <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 index 000000000..8747deac6 --- /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; +} -- 2.26.2