libc has a number of macros for dealing with thread safety such that it
can operate efficiently when single-threaded but Do The Right Thing when
multi-threaded. In include/thread_private.h are two sets of macros that
look interchangable but that are quite different on the underside.
_MUTEX_LOCK() and _MUTEX_UNLOCK() let libc treat a void* variable as a
mutex. They're no-ops unless linked with libpthread.
_THREAD_PRIVATE_MUTEX_LOCK() and _THREAD_PRIVATE_MUTEX_UNLOCK() look
similar, but require you to declare the mutex with _THREAD_PRIVATE_MUTEX()
and have this _THREAD_PRIVATE() extra feature for doing thread-specific
data.
The trick is that the _THREAD_PRIVATE() feature means
_THREAD_PRIVATE_MUTEX_LOCK() is quite a bit more expensive, allocating a
couple more chunks of memory and creating a pthread_key_t under the
covers, which involves another spin lock, etc. If you're not using the
per-thread storage part of _THREAD_PRIVATE* then it's a pile of overhead
and over kill.
So, diff below converts several uses of _THREAD_PRIVATE_MUTEX_*() to
_MUTEX_*(). Regress tests libc/stdio_threading/* and asr/bin/threads
still pass with this.
ok?
Philip Guenther
Index: stdio/findfp.c
===================================================================
RCS file: /cvs/src/lib/libc/stdio/findfp.c,v
retrieving revision 1.18
diff -u -p -r1.18 findfp.c
--- stdio/findfp.c 27 Aug 2015 04:37:09 -0000 1.18
+++ stdio/findfp.c 4 Apr 2016 00:47:53 -0000
@@ -56,7 +56,7 @@ static FILE usual[FOPEN_MAX - 3];
static struct __sfileext usualext[FOPEN_MAX - 3];
static struct glue uglue = { 0, FOPEN_MAX - 3, usual };
static struct glue *lastglue = &uglue;
-_THREAD_PRIVATE_MUTEX(__sfp_mutex);
+static void *sfp_mutex;
static struct __sfileext __sFext[3];
FILE __sF[3] = {
@@ -108,7 +108,7 @@ __sfp(void)
if (!__sdidinit)
__sinit();
- _THREAD_PRIVATE_MUTEX_LOCK(__sfp_mutex);
+ _MUTEX_LOCK(&sfp_mutex);
for (g = &__sglue; g != NULL; g = g->next) {
for (fp = g->iobs, n = g->niobs; --n >= 0; fp++)
if (fp->_flags == 0)
@@ -116,16 +116,16 @@ __sfp(void)
}
/* release lock while mallocing */
- _THREAD_PRIVATE_MUTEX_UNLOCK(__sfp_mutex);
+ _MUTEX_UNLOCK(&sfp_mutex);
if ((g = moreglue(NDYNAMIC)) == NULL)
return (NULL);
- _THREAD_PRIVATE_MUTEX_LOCK(__sfp_mutex);
+ _MUTEX_LOCK(&sfp_mutex);
lastglue->next = g;
lastglue = g;
fp = g->iobs;
found:
fp->_flags = 1; /* reserve this slot; caller sets real flags */
- _THREAD_PRIVATE_MUTEX_UNLOCK(__sfp_mutex);
+ _MUTEX_UNLOCK(&sfp_mutex);
fp->_p = NULL; /* no current pointer */
fp->_w = 0; /* nothing to read or write */
fp->_r = 0;
@@ -161,10 +161,10 @@ _cleanup(void)
void
__sinit(void)
{
- _THREAD_PRIVATE_MUTEX(__sinit_mutex);
+ static void *sinit_mutex;
int i;
- _THREAD_PRIVATE_MUTEX_LOCK(__sinit_mutex);
+ _MUTEX_LOCK(&sinit_mutex);
if (__sdidinit)
goto out; /* bail out if caller lost the race */
for (i = 0; i < FOPEN_MAX - 3; i++) {
@@ -174,5 +174,5 @@ __sinit(void)
__atexit_register_cleanup(_cleanup); /* conservative */
__sdidinit = 1;
out:
- _THREAD_PRIVATE_MUTEX_UNLOCK(__sinit_mutex);
+ _MUTEX_UNLOCK(&sinit_mutex);
}
Index: stdlib/random.c
===================================================================
RCS file: /cvs/src/lib/libc/stdlib/random.c,v
retrieving revision 1.29
diff -u -p -r1.29 random.c
--- stdlib/random.c 16 Jan 2015 16:48:51 -0000 1.29
+++ stdlib/random.c 4 Apr 2016 00:47:53 -0000
@@ -176,10 +176,11 @@ static int rand_sep = SEP_3;
static int random_deterministic;
_THREAD_PRIVATE_MUTEX(random);
+static void *random_mutex;
static long random_l(void);
-#define LOCK() _THREAD_PRIVATE_MUTEX_LOCK(random)
-#define UNLOCK() _THREAD_PRIVATE_MUTEX_UNLOCK(random)
+#define LOCK() _MUTEX_LOCK(&random_mutex)
+#define UNLOCK() _MUTEX_UNLOCK(&random_mutex)
/*
* srandom:
Index: asr/res_init.c
===================================================================
RCS file: /cvs/src/lib/libc/asr/res_init.c,v
retrieving revision 1.9
diff -u -p -r1.9 res_init.c
--- asr/res_init.c 23 Mar 2016 18:45:03 -0000 1.9
+++ asr/res_init.c 4 Apr 2016 00:47:53 -0000
@@ -37,7 +37,7 @@ int h_errno;
int
res_init(void)
{
- _THREAD_PRIVATE_MUTEX(init);
+ static void *resinit_mutex;
struct asr_ctx *ac;
int i;
@@ -48,7 +48,7 @@ res_init(void)
* structure from the async context, not overriding fields set early
* by the user.
*/
- _THREAD_PRIVATE_MUTEX_LOCK(init);
+ _MUTEX_LOCK(&resinit_mutex);
if (!(_res.options & RES_INIT)) {
if (_res.retry == 0)
_res.retry = ac->ac_nsretries;
@@ -75,7 +75,7 @@ res_init(void)
_res.nscount = i;
_res.options |= RES_INIT;
}
- _THREAD_PRIVATE_MUTEX_UNLOCK(init);
+ _MUTEX_UNLOCK(&resinit_mutex);
/*
* If the program is not threaded, we want to reflect (some) changes
Index: net/res_random.c
===================================================================
RCS file: /cvs/src/lib/libc/net/res_random.c,v
retrieving revision 1.23
diff -u -p -r1.23 res_random.c
--- net/res_random.c 5 Oct 2015 02:57:16 -0000 1.23
+++ net/res_random.c 4 Apr 2016 00:47:53 -0000
@@ -230,12 +230,12 @@ __res_randomid(void)
struct timespec ts;
pid_t pid;
u_int r;
- _THREAD_PRIVATE_MUTEX(random);
+ static void *randomid_mutex;
clock_gettime(CLOCK_MONOTONIC, &ts);
pid = getpid();
- _THREAD_PRIVATE_MUTEX_LOCK(random);
+ _MUTEX_LOCK(&randomid_mutex);
if (ru_counter >= RU_MAX || ts.tv_sec > ru_reseed || pid != ru_pid) {
res_initid();
@@ -248,7 +248,7 @@ __res_randomid(void)
r = permute15(ru_seed ^ pmod(ru_g, ru_seed2 + ru_x, RU_N)) | ru_msb;
- _THREAD_PRIVATE_MUTEX_UNLOCK(random);
+ _MUTEX_UNLOCK(&randomid_mutex);
return (r);
}
