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index-pack: work around thread-unsafe pread() 

Multi-threaing of index-pack was disabled with c0f8654
(index-pack: Disable threading on cygwin - 2012-06-26), because
pread() implementations for Cygwin and MSYS were not thread
safe.  Recent Cygwin does offer usable pread() and we enabled
multi-threading with 103d530f (Cygwin 1.7 has thread-safe pread,
2013-07-19).

Work around this problem on platforms with a thread-unsafe
pread() emulation by opening one file handle per thread; it
would prevent parallel pread() on different file handles from
stepping on each other.

Also remove NO_THREAD_SAFE_PREAD that was introduced in c0f8654
because it's no longer used anywhere.

This workaround is unconditional, even for platforms with
thread-safe pread() because the overhead is small (a couple file
handles more) and not worth fragmenting the code.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Tested-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy 2014-03-25 20:41:41 +07:00 committed by Junio C Hamano
parent 5f95c9f850
commit 39539495ac
3 changed files with 17 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Makefile
View File

@ -191,9 +191,6 @@ all::
# Define NO_STRUCT_ITIMERVAL if you don't have struct itimerval
# This also implies NO_SETITIMER
#
# Define NO_THREAD_SAFE_PREAD if your pread() implementation is not
# thread-safe. (e.g. compat/pread.c or cygwin)
#
# Define NO_FAST_WORKING_DIRECTORY if accessing objects in pack files is
# generally faster on your platform than accessing the working directory.
#
@ -1341,10 +1338,6 @@ endif
ifdef NO_PREAD
COMPAT_CFLAGS += -DNO_PREAD
COMPAT_OBJS += compat/pread.o
NO_THREAD_SAFE_PREAD = YesPlease
endif
ifdef NO_THREAD_SAFE_PREAD
BASIC_CFLAGS += -DNO_THREAD_SAFE_PREAD
endif
ifdef NO_FAST_WORKING_DIRECTORY
BASIC_CFLAGS += -DNO_FAST_WORKING_DIRECTORY

27
builtin/index-pack.c
View File

@ -40,17 +40,13 @@ struct base_data {
int ofs_first, ofs_last;
};
#if !defined(NO_PTHREADS) && defined(NO_THREAD_SAFE_PREAD)
/* pread() emulation is not thread-safe. Disable threading. */
#define NO_PTHREADS
#endif
struct thread_local {
#ifndef NO_PTHREADS
pthread_t thread;
#endif
struct base_data *base_cache;
size_t base_cache_used;
int pack_fd;
};
/*
@ -91,7 +87,8 @@ static off_t consumed_bytes;
static unsigned deepest_delta;
static git_SHA_CTX input_ctx;
static uint32_t input_crc32;
static int input_fd, output_fd, pack_fd;
static int input_fd, output_fd;
static const char *curr_pack;
#ifndef NO_PTHREADS
@ -134,6 +131,7 @@ static inline void unlock_mutex(pthread_mutex_t *mutex)
*/
static void init_thread(void)
{
int i;
init_recursive_mutex(&read_mutex);
pthread_mutex_init(&counter_mutex, NULL);
pthread_mutex_init(&work_mutex, NULL);
@ -141,11 +139,18 @@ static void init_thread(void)
pthread_mutex_init(&deepest_delta_mutex, NULL);
pthread_key_create(&key, NULL);
thread_data = xcalloc(nr_threads, sizeof(*thread_data));
for (i = 0; i < nr_threads; i++) {
thread_data[i].pack_fd = open(curr_pack, O_RDONLY);
if (thread_data[i].pack_fd == -1)
die_errno(_("unable to open %s"), curr_pack);
}
threads_active = 1;
}
static void cleanup_thread(void)
{
int i;
if (!threads_active)
return;
threads_active = 0;
@ -154,6 +159,8 @@ static void cleanup_thread(void)
pthread_mutex_destroy(&work_mutex);
if (show_stat)
pthread_mutex_destroy(&deepest_delta_mutex);
for (i = 0; i < nr_threads; i++)
close(thread_data[i].pack_fd);
pthread_key_delete(key);
free(thread_data);
}
@ -288,13 +295,13 @@ static const char *open_pack_file(const char *pack_name)
output_fd = open(pack_name, O_CREAT|O_EXCL|O_RDWR, 0600);
if (output_fd < 0)
die_errno(_("unable to create '%s'"), pack_name);
pack_fd = output_fd;
nothread_data.pack_fd = output_fd;
} else {
input_fd = open(pack_name, O_RDONLY);
if (input_fd < 0)
die_errno(_("cannot open packfile '%s'"), pack_name);
output_fd = -1;
pack_fd = input_fd;
nothread_data.pack_fd = input_fd;
}
git_SHA1_Init(&input_ctx);
return pack_name;
@ -542,7 +549,7 @@ static void *unpack_data(struct object_entry *obj,
do {
ssize_t n = (len < 64*1024) ? len : 64*1024;
n = pread(pack_fd, inbuf, n, from);
n = pread(get_thread_data()->pack_fd, inbuf, n, from);
if (n < 0)
die_errno(_("cannot pread pack file"));
if (!n)
@ -1490,7 +1497,7 @@ static void show_pack_info(int stat_only)
int cmd_index_pack(int argc, const char **argv, const char *prefix)
{
int i, fix_thin_pack = 0, verify = 0, stat_only = 0;
const char *curr_pack, *curr_index;
const char *curr_index;
const char *index_name = NULL, *pack_name = NULL;
const char *keep_name = NULL, *keep_msg = NULL;
char *index_name_buf = NULL, *keep_name_buf = NULL;

1
config.mak.uname
View File

@ -158,7 +158,6 @@ ifeq ($(uname_O),Cygwin)
NO_SYMLINK_HEAD = YesPlease
NO_IPV6 = YesPlease
OLD_ICONV = UnfortunatelyYes
NO_THREAD_SAFE_PREAD = YesPlease
# There are conflicting reports about this.
# On some boxes NO_MMAP is needed, and not so elsewhere.
# Try commenting this out if you suspect MMAP is more efficient