git@vger.kernel.org mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: "Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
To: pclouds@gmail.com
Cc: git@vger.kernel.org, gitster@pobox.com, peartben@gmail.com,
	peff@peff.net
Subject: [PATCH v3 01/14] thread-utils: macros to unconditionally compile pthreads API
Date: Sat,  3 Nov 2018 09:48:37 +0100	[thread overview]
Message-ID: <20181103084850.9584-2-pclouds@gmail.com> (raw)
In-Reply-To: <20181103084850.9584-1-pclouds@gmail.com>

When built with NO_PTHREADS, the macros are used make the code build
even though pthreads header and library may be missing. The code can
still have different code paths for no threads support with
HAVE_THREADS variable.

There are of course impacts on no-pthreads builds:

- data structure may get slightly bigger because all the mutexes and
  pthread_t are present (as an int)

- code execution is not impacted much. Locking (in hot path) is
  no-op. Other wrapper function calls really should not matter much.

- the binary size grows bigger because of threaded code. But at least
  on Linux this does not matter, if some code is not executed, it's
  not mapped in memory.

This is a preparation step to remove "#ifdef NO_PTHREADS" in the code
mostly because of maintainability. As Jeff put it

> it's probably OK to stop thinking of it as "non-threaded platforms
> are the default and must pay zero cost" and more as "threaded
> platforms are the default, and non-threaded ones are OK to pay a
> small cost as long as they still work".

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Makefile       |  2 +-
 thread-utils.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 thread-utils.h | 48 +++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 94 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index b08d5ea258..321540a736 100644
--- a/Makefile
+++ b/Makefile
@@ -991,6 +991,7 @@ LIB_OBJS += sub-process.o
 LIB_OBJS += symlinks.o
 LIB_OBJS += tag.o
 LIB_OBJS += tempfile.o
+LIB_OBJS += thread-utils.o
 LIB_OBJS += tmp-objdir.o
 LIB_OBJS += trace.o
 LIB_OBJS += trailer.o
@@ -1674,7 +1675,6 @@ ifdef NO_PTHREADS
 else
 	BASIC_CFLAGS += $(PTHREAD_CFLAGS)
 	EXTLIBS += $(PTHREAD_LIBS)
-	LIB_OBJS += thread-utils.o
 endif
 
 ifdef HAVE_PATHS_H
diff --git a/thread-utils.c b/thread-utils.c
index a2135e0743..5329845691 100644
--- a/thread-utils.c
+++ b/thread-utils.c
@@ -20,6 +20,9 @@
 
 int online_cpus(void)
 {
+#ifdef NO_PTHREADS
+	return 1;
+#else
 #ifdef _SC_NPROCESSORS_ONLN
 	long ncpus;
 #endif
@@ -59,10 +62,12 @@ int online_cpus(void)
 #endif
 
 	return 1;
+#endif
 }
 
 int init_recursive_mutex(pthread_mutex_t *m)
 {
+#ifndef NO_PTHREADS
 	pthread_mutexattr_t a;
 	int ret;
 
@@ -74,4 +79,47 @@ int init_recursive_mutex(pthread_mutex_t *m)
 		pthread_mutexattr_destroy(&a);
 	}
 	return ret;
+#else
+	return 0;
+#endif
+}
+
+#ifdef NO_PTHREADS
+int dummy_pthread_create(pthread_t *pthread, const void *attr,
+			 void *(*fn)(void *), void *data)
+{
+	/*
+	 * Do nothing.
+	 *
+	 * The main purpose of this function is to break compiler's
+	 * flow analysis and avoid -Wunused-variable false warnings.
+	 */
+	return ENOSYS;
+}
+
+int dummy_pthread_init(void *data)
+{
+	/*
+	 * Do nothing.
+	 *
+	 * The main purpose of this function is to break compiler's
+	 * flow analysis or it may realize that functions like
+	 * pthread_mutex_init() is no-op, which means the (static)
+	 * variable is not used/initialized at all and trigger
+	 * -Wunused-variable
+	 */
+	return ENOSYS;
 }
+
+int dummy_pthread_join(pthread_t pthread, void **retval)
+{
+	/*
+	 * Do nothing.
+	 *
+	 * The main purpose of this function is to break compiler's
+	 * flow analysis and avoid -Wunused-variable false warnings.
+	 */
+	return ENOSYS;
+}
+
+#endif
diff --git a/thread-utils.h b/thread-utils.h
index d9a769d190..4961487ed9 100644
--- a/thread-utils.h
+++ b/thread-utils.h
@@ -4,12 +4,54 @@
 #ifndef NO_PTHREADS
 #include <pthread.h>
 
-extern int online_cpus(void);
-extern int init_recursive_mutex(pthread_mutex_t*);
+#define HAVE_THREADS 1
 
 #else
 
-#define online_cpus() 1
+#define HAVE_THREADS 0
+
+/*
+ * macros instead of typedefs because pthread definitions may have
+ * been pulled in by some system dependencies even though the user
+ * wants to disable pthread.
+ */
+#define pthread_t int
+#define pthread_mutex_t int
+#define pthread_cond_t int
+#define pthread_key_t int
+
+#define pthread_mutex_init(mutex, attr) dummy_pthread_init(mutex)
+#define pthread_mutex_lock(mutex)
+#define pthread_mutex_unlock(mutex)
+#define pthread_mutex_destroy(mutex)
+
+#define pthread_cond_init(cond, attr) dummy_pthread_init(cond)
+#define pthread_cond_wait(cond, mutex)
+#define pthread_cond_signal(cond)
+#define pthread_cond_broadcast(cond)
+#define pthread_cond_destroy(cond)
+
+#define pthread_key_create(key, attr) dummy_pthread_init(key)
+#define pthread_key_delete(key)
+
+#define pthread_create(thread, attr, fn, data) \
+	dummy_pthread_create(thread, attr, fn, data)
+#define pthread_join(thread, retval) \
+	dummy_pthread_join(thread, retval)
+
+#define pthread_setspecific(key, data)
+#define pthread_getspecific(key) NULL
+
+int dummy_pthread_create(pthread_t *pthread, const void *attr,
+			 void *(*fn)(void *), void *data);
+int dummy_pthread_join(pthread_t pthread, void **retval);
+
+int dummy_pthread_init(void *);
 
 #endif
+
+int online_cpus(void);
+int init_recursive_mutex(pthread_mutex_t*);
+
+
 #endif /* THREAD_COMPAT_H */
-- 
2.19.1.1005.gac84295441


  reply	other threads:[~2018-11-03  8:49 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-27  7:09 [PATCH 00/10] Reduce #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-10-27  7:09 ` [PATCH 01/10] thread-utils: macros to unconditionally compile pthreads API Nguyễn Thái Ngọc Duy
2018-10-27  7:31   ` Jeff King
2018-10-27  7:40     ` Duy Nguyen
2018-10-27  8:15       ` Jeff King
2018-10-27 14:43         ` Duy Nguyen
2018-10-27  7:09 ` [PATCH 02/10] index-pack: remove #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-10-27  7:34   ` Jeff King
2018-10-27  7:09 ` [PATCH 03/10] name-hash.c: " Nguyễn Thái Ngọc Duy
2018-10-27  7:09 ` [PATCH 04/10] attr.c: " Nguyễn Thái Ngọc Duy
2018-10-27  7:09 ` [PATCH 05/10] send-pack.c: " Nguyễn Thái Ngọc Duy
2018-10-27  7:39   ` Jeff King
2018-10-27  7:09 ` [PATCH 06/10] grep: " Nguyễn Thái Ngọc Duy
2018-10-27  7:44   ` Jeff King
2018-10-29  2:16     ` Junio C Hamano
2018-10-29 14:25       ` Jeff King
2018-10-29 16:01         ` Duy Nguyen
2018-10-29 16:20           ` Jeff King
2018-10-30  1:27             ` Junio C Hamano
2018-10-27  7:10 ` [PATCH 07/10] preload-index.c: " Nguyễn Thái Ngọc Duy
2018-10-29 16:52   ` Ben Peart
2018-10-27  7:10 ` [PATCH 08/10] pack-objects: " Nguyễn Thái Ngọc Duy
2018-10-27  7:10 ` [PATCH 09/10] read-cache.c: " Nguyễn Thái Ngọc Duy
2018-10-29 17:05   ` Ben Peart
2018-10-29 17:21     ` Duy Nguyen
2018-10-29 17:58       ` Ben Peart
2018-10-30  1:44       ` Junio C Hamano
2018-10-27  7:10 ` [PATCH 10/10] Clean up pthread_create() error handling Nguyễn Thái Ngọc Duy
2018-10-27  7:24 ` [PATCH 00/10] Reduce #ifdef NO_PTHREADS Jeff King
2018-10-27  8:13 ` Jeff King
2018-10-27 17:07   ` Duy Nguyen
2018-10-27 17:29 ` [PATCH v2 " Nguyễn Thái Ngọc Duy
2018-10-27 17:29   ` [PATCH v2 01/10] thread-utils: macros to unconditionally compile pthreads API Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 02/10] index-pack: remove #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 03/10] name-hash.c: " Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 04/10] attr.c: " Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 05/10] grep: " Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 06/10] preload-index.c: " Nguyễn Thái Ngọc Duy
2018-10-29 17:21     ` Ben Peart
2018-10-29 17:26       ` Duy Nguyen
2018-10-29 18:05         ` Ben Peart
2018-10-29 20:11           ` Jeff King
2018-10-27 17:30   ` [PATCH v2 07/10] pack-objects: " Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 08/10] read-cache.c: " Nguyễn Thái Ngọc Duy
2018-10-29 14:30     ` Jeff King
2018-10-29 17:07       ` Ben Peart
2018-10-29 17:23       ` Ben Peart
2018-10-27 17:30   ` [PATCH v2 09/10] Clean up pthread_create() error handling Nguyễn Thái Ngọc Duy
2018-10-27 17:30   ` [PATCH v2 10/10] read-cache.c: initialize copy_len to shut up gcc 8 Nguyễn Thái Ngọc Duy
2018-10-29 14:31     ` Jeff King
2018-11-03  8:48   ` [PATCH v3 00/14] Reduce #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` Nguyễn Thái Ngọc Duy [this message]
2018-11-03  8:48     ` [PATCH v3 02/14] run-command.h: include thread-utils.h instead of pthread.h Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 03/14] send-pack.c: move async's #ifdef NO_PTHREADS back to run-command.c Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 04/14] index-pack: remove #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 05/14] name-hash.c: " Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 06/14] attr.c: " Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 07/14] grep: " Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 08/14] grep: clean up num_threads handling Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 09/14] preload-index.c: remove #ifdef NO_PTHREADS Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 10/14] pack-objects: " Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 11/14] read-cache.c: " Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 12/14] read-cache.c: reduce branching based on HAVE_THREADS Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 13/14] read-cache.c: initialize copy_len to shut up gcc 8 Nguyễn Thái Ngọc Duy
2018-11-03  8:48     ` [PATCH v3 14/14] Clean up pthread_create() error handling Nguyễn Thái Ngọc Duy
2018-11-06  4:51     ` [PATCH v3 00/14] Reduce #ifdef NO_PTHREADS Junio C Hamano

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181103084850.9584-2-pclouds@gmail.com \
    --to=pclouds@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=peartben@gmail.com \
    --cc=peff@peff.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).