Paul Eggert wrote:
> True enough, but how about suggesting that people write something like the
> following?
>
> bool mt = gl_multithreaded ();
> if (mt) gl_lock_lock (file_cleanup_list_lock);
> ...
> if (mt) gl_lock_unlock (file_cleanup_list_lock);
>
> This is nearly as concise as the IF_MT_DECL and IF_MT macros, allows for
> further
> enhancements by builtin_expect etc., and avoids the macro hackery.
Indeed. With only function-like macros, the source code is more transparent
and probably as future-proof.
I'm applying your suggestion.
2020-08-12 Bruno Haible <br...@clisp.org>
thread-optim: Export function-like macros only.
Suggested by Paul Eggert.
* lib/thread-optim.h (gl_multithreaded): New macro.
(IF_MT_DECL, IF_MT): Remove macros.
* doc/multithread.texi (Multithreading Optimizations): Add a small
example.
* lib/fatal-signal.c: Update all uses.
* lib/clean-temp.c: Likewise.
* lib/localename.c: Likewise.
* modules/localename (Depends-on): Add stdbool.
diff --git a/lib/thread-optim.h b/lib/thread-optim.h
index 0cdcfec..b649c50 100644
--- a/lib/thread-optim.h
+++ b/lib/thread-optim.h
@@ -26,23 +26,25 @@
/* Typical use: In a block or function, use
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
...
- IF_MT
+ if (mt)
if (pthread_mutex_lock (&lock)) abort ();
...
- IF_MT
+ if (mt)
if (pthread_mutex_unlock (&lock)) abort ();
- The macro IF_MT_DECL establishes local variables for use by IF_MT.
+ The gl_multithreaded () invocation determines whether the program currently
+ is multithreaded.
- IF_MT STATEMENT executes STATEMENT in the multithreaded cases, and skips it
- in the single-threaded case.
+ if (mt) STATEMENT executes STATEMENT in the multithreaded case, and skips
+ it in the single-threaded case.
- The code between IF_MT_DECL and IF_MT must not create threads or invoke
- functions that may indirectly create threads (e.g. 'dlopen' may, indirectly
- through C++ initializers of global variables in the shared library being
- opened, create threads).
+ The code between the gl_multithreaded () invocation and any use of the
+ variable 'mt' must not create threads or invoke functions that may
+ indirectly create threads (e.g. 'dlopen' may, indirectly through C++
+ initializers of global variables in the shared library being opened,
+ create threads).
The lock here is meant to synchronize threads in the same process. The
same optimization cannot be applied to locks that synchronize different
@@ -50,11 +52,9 @@
#if HAVE_SYS_SINGLE_THREADED_H /* glibc >= 2.32 */
# include <sys/single_threaded.h>
-# define IF_MT_DECL char optimize_for_single_thread = __libc_single_threaded
-# define IF_MT if (!optimize_for_single_thread)
+# define gl_multithreaded() !__libc_single_threaded
#else
-# define IF_MT_DECL (void)0
-# define IF_MT
+# define gl_multithreaded() 1
#endif
#endif /* _THREAD_OPTIM_H */
diff --git a/doc/multithread.texi b/doc/multithread.texi
index 022a6cb..9b1bc2e 100644
--- a/doc/multithread.texi
+++ b/doc/multithread.texi
@@ -249,8 +249,14 @@ to all the Gnulib multithreading API (locks, thread-local
storage, and more).
The @code{thread-optim} module, on glibc @geq{} 2.32 systems, allows your code
to skip locking between threads (regardless which of the three multithreading
APIs you use). You need extra code for this: include the
-@code{"thread-optim.h"} header file, and use the macros @code{IF_MT_DECL}
-and @code{IF_MT}.
+@code{"thread-optim.h"} header file, and use the macro @code{gl_multithreaded}
+like this:
+@smallexample
+bool mt = gl_multithreaded ();
+if (mt) gl_lock_lock (some_lock);
+...
+if (mt) gl_lock_unlock (some_lock);
+@end smallexample
@item
The @code{unlocked-io} module is applicable only if all the programs in your
package are single-threaded. It optimizes the operations on @code{FILE}
diff --git a/lib/clean-temp.c b/lib/clean-temp.c
index 605390b..4a992c4 100644
--- a/lib/clean-temp.c
+++ b/lib/clean-temp.c
@@ -407,9 +407,9 @@ init_clean_temp (void)
void
register_temporary_file (const char *absolute_file_name)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (file_cleanup_list_lock);
+ if (mt) gl_lock_lock (file_cleanup_list_lock);
/* Make sure that this facility and the file_cleanup_list are initialized.
*/
if (file_cleanup_list == NULL)
@@ -424,7 +424,7 @@ register_temporary_file (const char *absolute_file_name)
if (gl_list_search (file_cleanup_list, absolute_file_name) == NULL)
gl_list_add_first (file_cleanup_list, xstrdup (absolute_file_name));
- IF_MT gl_lock_unlock (file_cleanup_list_lock);
+ if (mt) gl_lock_unlock (file_cleanup_list_lock);
}
/* Unregister the given ABSOLUTE_FILE_NAME as being a file that needs to be
@@ -433,9 +433,9 @@ register_temporary_file (const char *absolute_file_name)
void
unregister_temporary_file (const char *absolute_file_name)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (file_cleanup_list_lock);
+ if (mt) gl_lock_lock (file_cleanup_list_lock);
gl_list_t list = file_cleanup_list;
if (list != NULL)
@@ -450,7 +450,7 @@ unregister_temporary_file (const char *absolute_file_name)
}
}
- IF_MT gl_lock_unlock (file_cleanup_list_lock);
+ if (mt) gl_lock_unlock (file_cleanup_list_lock);
}
/* Remove a file, with optional error message.
@@ -498,9 +498,9 @@ struct temp_dir *
create_temp_dir (const char *prefix, const char *parentdir,
bool cleanup_verbose)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
struct tempdir * volatile *tmpdirp = NULL;
struct tempdir *tmpdir;
@@ -607,12 +607,12 @@ create_temp_dir (const char *prefix, const char
*parentdir,
block because then the cleanup handler would not remove the directory
if xstrdup fails. */
tmpdir->dirname = xstrdup (tmpdirname);
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
freea (xtemplate);
return (struct temp_dir *) tmpdir;
quit:
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
freea (xtemplate);
return NULL;
}
@@ -625,15 +625,15 @@ register_temp_file (struct temp_dir *dir,
const char *absolute_file_name)
{
struct tempdir *tmpdir = (struct tempdir *)dir;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
/* Add absolute_file_name to tmpdir->files, without duplicates. */
if (gl_list_search (tmpdir->files, absolute_file_name) == NULL)
gl_list_add_first (tmpdir->files, xstrdup (absolute_file_name));
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
}
/* Unregister the given ABSOLUTE_FILE_NAME as being a file inside DIR, that
@@ -644,9 +644,9 @@ unregister_temp_file (struct temp_dir *dir,
const char *absolute_file_name)
{
struct tempdir *tmpdir = (struct tempdir *)dir;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
gl_list_t list = tmpdir->files;
gl_list_node_t node;
@@ -660,7 +660,7 @@ unregister_temp_file (struct temp_dir *dir,
free (old_string);
}
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
}
/* Register the given ABSOLUTE_DIR_NAME as being a subdirectory inside DIR,
@@ -671,15 +671,15 @@ register_temp_subdir (struct temp_dir *dir,
const char *absolute_dir_name)
{
struct tempdir *tmpdir = (struct tempdir *)dir;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
/* Add absolute_dir_name to tmpdir->subdirs, without duplicates. */
if (gl_list_search (tmpdir->subdirs, absolute_dir_name) == NULL)
gl_list_add_first (tmpdir->subdirs, xstrdup (absolute_dir_name));
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
}
/* Unregister the given ABSOLUTE_DIR_NAME as being a subdirectory inside DIR,
@@ -691,9 +691,9 @@ unregister_temp_subdir (struct temp_dir *dir,
const char *absolute_dir_name)
{
struct tempdir *tmpdir = (struct tempdir *)dir;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
gl_list_t list = tmpdir->subdirs;
gl_list_node_t node;
@@ -707,7 +707,7 @@ unregister_temp_subdir (struct temp_dir *dir,
free (old_string);
}
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
}
/* Remove a directory, with optional error message.
@@ -803,9 +803,9 @@ cleanup_temp_dir_contents (struct temp_dir *dir)
int
cleanup_temp_dir (struct temp_dir *dir)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (dir_cleanup_list_lock);
+ if (mt) gl_lock_lock (dir_cleanup_list_lock);
struct tempdir *tmpdir = (struct tempdir *)dir;
int err = 0;
@@ -832,7 +832,7 @@ cleanup_temp_dir (struct temp_dir *dir)
gl_list_free (tmpdir->subdirs);
free (tmpdir->dirname);
free (tmpdir);
- IF_MT gl_lock_unlock (dir_cleanup_list_lock);
+ if (mt) gl_lock_unlock (dir_cleanup_list_lock);
return err;
}
@@ -879,9 +879,9 @@ supports_delete_on_close ()
static void
register_fd (int fd)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (descriptors_lock);
+ if (mt) gl_lock_lock (descriptors_lock);
if (descriptors == NULL)
descriptors = gl_list_create_empty (GL_LINKED_LIST, NULL, NULL, NULL,
@@ -895,7 +895,7 @@ register_fd (int fd)
gl_list_add_first (descriptors, element);
- IF_MT gl_lock_unlock (descriptors_lock);
+ if (mt) gl_lock_unlock (descriptors_lock);
}
/* Open a temporary file in a temporary directory.
@@ -1041,9 +1041,9 @@ close_temp (int fd)
int result = 0;
int saved_errno = 0;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (descriptors_lock);
+ if (mt) gl_lock_lock (descriptors_lock);
gl_list_t list = descriptors;
if (list == NULL)
@@ -1089,7 +1089,7 @@ close_temp (int fd)
/* descriptors should already contain fd. */
abort ();
- IF_MT gl_lock_unlock (descriptors_lock);
+ if (mt) gl_lock_unlock (descriptors_lock);
errno = saved_errno;
return result;
@@ -1105,9 +1105,9 @@ fclose_variant_temp (FILE *fp, int (*fclose_variant)
(FILE *))
int result = 0;
int saved_errno = 0;
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (descriptors_lock);
+ if (mt) gl_lock_lock (descriptors_lock);
gl_list_t list = descriptors;
if (list == NULL)
@@ -1153,7 +1153,7 @@ fclose_variant_temp (FILE *fp, int (*fclose_variant)
(FILE *))
/* descriptors should have contained fd. */
abort ();
- IF_MT gl_lock_unlock (descriptors_lock);
+ if (mt) gl_lock_unlock (descriptors_lock);
errno = saved_errno;
return result;
diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c
index 541c4cb..14ecfe7 100644
--- a/lib/fatal-signal.c
+++ b/lib/fatal-signal.c
@@ -214,9 +214,9 @@ gl_lock_define_initialized (static, at_fatal_signal_lock)
void
at_fatal_signal (action_t action)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (at_fatal_signal_lock);
+ if (mt) gl_lock_lock (at_fatal_signal_lock);
static bool cleanup_initialized = false;
if (!cleanup_initialized)
@@ -263,7 +263,7 @@ at_fatal_signal (action_t action)
actions[actions_count].action = action;
actions_count++;
- IF_MT gl_lock_unlock (at_fatal_signal_lock);
+ if (mt) gl_lock_unlock (at_fatal_signal_lock);
}
@@ -303,9 +303,9 @@ static unsigned int fatal_signals_block_counter = 0;
void
block_fatal_signals (void)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (fatal_signals_block_lock);
+ if (mt) gl_lock_lock (fatal_signals_block_lock);
if (fatal_signals_block_counter++ == 0)
{
@@ -313,16 +313,16 @@ block_fatal_signals (void)
sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL);
}
- IF_MT gl_lock_unlock (fatal_signals_block_lock);
+ if (mt) gl_lock_unlock (fatal_signals_block_lock);
}
/* Stop delaying the catchable fatal signals. */
void
unblock_fatal_signals (void)
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
- IF_MT gl_lock_lock (fatal_signals_block_lock);
+ if (mt) gl_lock_lock (fatal_signals_block_lock);
if (fatal_signals_block_counter == 0)
/* There are more calls to unblock_fatal_signals() than to
@@ -334,7 +334,7 @@ unblock_fatal_signals (void)
sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);
}
- IF_MT gl_lock_unlock (fatal_signals_block_lock);
+ if (mt) gl_lock_unlock (fatal_signals_block_lock);
}
diff --git a/lib/localename.c b/lib/localename.c
index 2e76c11..5731ceb 100644
--- a/lib/localename.c
+++ b/lib/localename.c
@@ -28,6 +28,7 @@
#endif
#include <limits.h>
+#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <locale.h>
@@ -2699,9 +2700,9 @@ struniq (const char *string)
return "C";
memcpy (new_node->contents, string, size);
{
- IF_MT_DECL;
+ bool mt = gl_multithreaded ();
/* Lock while inserting new_node. */
- IF_MT gl_lock_lock (struniq_lock);
+ if (mt) gl_lock_lock (struniq_lock);
/* Check whether another thread already added the string while we were
waiting on the lock. */
for (p = struniq_hash_table[slot]; p != NULL; p = p->next)
@@ -2717,7 +2718,7 @@ struniq (const char *string)
struniq_hash_table[slot] = new_node;
done:
/* Unlock after new_node is inserted. */
- IF_MT gl_lock_unlock (struniq_lock);
+ if (mt) gl_lock_unlock (struniq_lock);
}
return new_node->contents;
}
diff --git a/modules/localename b/modules/localename
index 28710d0..b0e84e3 100644
--- a/modules/localename
+++ b/modules/localename
@@ -13,6 +13,7 @@ m4/lcmessage.m4
Depends-on:
extensions
+stdbool
locale
flexmember
strdup
