Use private futexes for pthread_mutex_t.
This does not change the implementation of conditional variables
since we're waiting for other system components to properly use
pthread_condattr_init/setpshared before that.
Also remove an obsolete x86 source file.
Change-Id: Ia3e3fbac35b87a534fb04d4381c3c66b975bc8f7
diff --git a/libc/arch-arm/bionic/atomics_arm.S b/libc/arch-arm/bionic/atomics_arm.S
index 55c642f..047541f 100644
--- a/libc/arch-arm/bionic/atomics_arm.S
+++ b/libc/arch-arm/bionic/atomics_arm.S
@@ -35,10 +35,6 @@
.type __atomic_dec, %function
.global __atomic_inc
.type __atomic_inc, %function
-.global __futex_wait
-.type __futex_wait, %function
-.global __futex_wake
-.type __futex_wake, %function
#define FUTEX_WAIT 0
#define FUTEX_WAKE 1
@@ -159,10 +155,34 @@
bx lr
/* __futex_wait(*ftx, val, *timespec) */
-/* __futex_syscall(*ftx, op, val, *timespec, *addr2, val3) */
+/* __futex_wake(*ftx, counter) */
+/* __futex_syscall3(*ftx, op, val) */
+/* __futex_syscall4(*ftx, op, val, *timespec) */
+
+.global __futex_wait
+.type __futex_wait, %function
+
+.global __futex_wake
+.type __futex_wake, %function
+
+.global __futex_syscall3
+.type __futex_syscall3, %function
+
+.global __futex_syscall4
+.type __futex_syscall4, %function
#if __ARM_EABI__
+__futex_syscall3:
+ .fnstart
+ stmdb sp!, {r4, r7}
+ .save {r4, r7}
+ ldr r7, =__NR_futex
+ swi #0
+ ldmia sp!, {r4, r7}
+ bx lr
+ .fnend
+
__futex_wait:
.fnstart
stmdb sp!, {r4, r7}
@@ -187,6 +207,10 @@
#else
+__futex_syscall3:
+ swi #__NR_futex
+ bx lr
+
__futex_wait:
mov r3, r2
mov r2, r1
@@ -201,3 +225,6 @@
bx lr
#endif
+
+__futex_syscall4:
+ b __futex_syscall3
diff --git a/libc/arch-sh/bionic/atomics_sh.c b/libc/arch-sh/bionic/atomics_sh.c
index 16966f7..c7815ff 100644
--- a/libc/arch-sh/bionic/atomics_sh.c
+++ b/libc/arch-sh/bionic/atomics_sh.c
@@ -98,3 +98,13 @@
{
return futex(ftx, FUTEX_WAKE, count, NULL, NULL, 0);
}
+
+int __futex_syscall3(volatile void *ftx, int op, int val)
+{
+ return futex(ftx, op, val, NULL, NULL, 0);
+}
+
+int __futex_syscall4(volative void *ftx, int op, int val, const struct timespec *timeout)
+{
+ return futex(ftx, op, val, (void *)timeout, NULL, 0);
+}
diff --git a/libc/arch-x86/bionic/atomics_x86.S b/libc/arch-x86/bionic/atomics_x86.S
index 2370f23..666e182 100644
--- a/libc/arch-x86/bionic/atomics_x86.S
+++ b/libc/arch-x86/bionic/atomics_x86.S
@@ -41,6 +41,38 @@
popl %ebx
ret
+/* int __futex_syscall3(volatile void *ftx, int op, int count) */
+.text
+.globl __futex_syscall3
+.type __futex_syscall3, @function
+.align 4
+__futex_syscall3:
+ pushl %ebx
+ movl 8(%esp), %ebx /* ftx */
+ movl 12(%esp), %ecx /* op */
+ movl 16(%esp), %edx /* value */
+ movl $__NR_futex, %eax
+ int $0x80
+ popl %ebx
+ ret
+
+/* int __futex_syscall4(volatile void *ftx, int op, int val, const struct timespec *timeout) */
+.text
+.globl __futex_syscall4
+.type __futex_syscall4, @function
+.align 4
+__futex_syscall4:
+ pushl %ebx
+ pushl %esi
+ movl 12(%esp), %ebx /* ftx */
+ movl 16(%esp), %ecx /* op */
+ movl 20(%esp), %edx /* val */
+ movl 24(%esp), %esi /* timeout */
+ movl $__NR_futex, %eax
+ int $0x80
+ popl %esi
+ popl %ebx
+ ret
/* int __atomic_cmpxchg(int old, int new, volatile int* addr) */
diff --git a/libc/arch-x86/bionic/atomics_x86.c b/libc/arch-x86/bionic/atomics_x86.c
deleted file mode 100644
index b7b20e6..0000000
--- a/libc/arch-x86/bionic/atomics_x86.c
+++ /dev/null
@@ -1,104 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * * Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in
- * the documentation and/or other materials provided with the
- * distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-#include <sys/atomics.h>
-
-#define FUTEX_SYSCALL 240
-#define FUTEX_WAIT 0
-#define FUTEX_WAKE 1
-
-int __futex_wait(volatile void *ftx, int val)
-{
- int ret;
- asm volatile (
- "int $0x80;"
- : "=a" (ret)
- : "0" (FUTEX_SYSCALL),
- "b" (ftx),
- "c" (FUTEX_WAIT),
- "d" (val),
- "S" (0)
- );
- return ret;
-}
-
-int __futex_wake(volatile void *ftx, int count)
-{
- int ret;
- asm volatile (
- "int $0x80;"
- : "=a" (ret)
- : "0" (FUTEX_SYSCALL),
- "b" (ftx),
- "c" (FUTEX_WAKE),
- "d" (count)
- );
- return ret;
-}
-
-int __atomic_cmpxchg(int old, int new, volatile int* addr) {
- int xchg;
- asm volatile (
- "lock;"
- "cmpxchg %%ecx, (%%edx);"
- "setne %%al;"
- : "=a" (xchg)
- : "a" (old),
- "c" (new),
- "d" (addr)
- );
- return xchg;
-}
-
-int __atomic_swap(int new, volatile int* addr) {
- int old;
- asm volatile (
- "lock;"
- "xchg %%ecx, (%%edx);"
- : "=c" (old)
- : "c" (new),
- "d" (addr)
- );
- return old;
-}
-
-int __atomic_dec(volatile int* addr) {
- int old;
- do {
- old = *addr;
- } while (atomic_cmpxchg(old, old-1, addr));
- return old;
-}
-
-int __atomic_inc(volatile int* addr) {
- int old;
- do {
- old = *addr;
- } while (atomic_cmpxchg(old, old+1, addr));
- return old;
-}
-
diff --git a/libc/bionic/pthread.c b/libc/bionic/pthread.c
index 4ffa9b8..3294cea 100644
--- a/libc/bionic/pthread.c
+++ b/libc/bionic/pthread.c
@@ -43,12 +43,16 @@
#include <memory.h>
#include <assert.h>
#include <malloc.h>
+#include <linux/futex.h>
extern int __pthread_clone(int (*fn)(void*), void *child_stack, int flags, void *arg);
extern void _exit_with_stack_teardown(void * stackBase, int stackSize, int retCode);
extern void _exit_thread(int retCode);
extern int __set_errno(int);
+#define __likely(cond) __builtin_expect(!!(cond), 1)
+#define __unlikely(cond) __builtin_expect(!!(cond), 0)
+
void _thread_created_hook(pid_t thread_id) __attribute__((noinline));
#define PTHREAD_ATTR_FLAG_DETACHED 0x00000001
@@ -712,6 +716,21 @@
int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
int __futex_wake(volatile void *ftx, int count);
+int __futex_syscall3(volatile void *ftx, int op, int val);
+int __futex_syscall4(volatile void *ftx, int op, int val, const struct timespec *timeout);
+
+#ifndef FUTEX_PRIVATE_FLAG
+#define FUTEX_PRIVATE_FLAG 128
+#endif
+
+#ifndef FUTEX_WAIT_PRIVATE
+#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
+#endif
+
+#ifndef FUTEX_WAKE_PRIVATE
+#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
+#endif
+
// mutex lock states
//
// 0: unlocked
@@ -723,7 +742,8 @@
* bits: name description
* 31-16 tid owner thread's kernel id (recursive and errorcheck only)
* 15-14 type mutex type
- * 13-2 counter counter of recursive mutexes
+ * 13 shared process-shared flag
+ * 12-2 counter counter of recursive mutexes
* 1-0 state lock state (0, 1 or 2)
*/
@@ -737,9 +757,17 @@
#define MUTEX_TYPE_ERRORCHECK 0x8000
#define MUTEX_COUNTER_SHIFT 2
-#define MUTEX_COUNTER_MASK 0x3ffc
+#define MUTEX_COUNTER_MASK 0x1ffc
+#define MUTEX_SHARED_MASK 0x2000
-
+/* a mutex attribute holds the following fields
+ *
+ * bits: name description
+ * 0-3 type type of mutex
+ * 4 shared process-shared flag
+ */
+#define MUTEXATTR_TYPE_MASK 0x000f
+#define MUTEXATTR_SHARED_MASK 0x0010
int pthread_mutexattr_init(pthread_mutexattr_t *attr)
@@ -764,10 +792,14 @@
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type)
{
- if (attr && *attr >= PTHREAD_MUTEX_NORMAL &&
- *attr <= PTHREAD_MUTEX_ERRORCHECK ) {
- *type = *attr;
- return 0;
+ if (attr) {
+ int atype = (*attr & MUTEXATTR_TYPE_MASK);
+
+ if (atype >= PTHREAD_MUTEX_NORMAL &&
+ atype <= PTHREAD_MUTEX_ERRORCHECK) {
+ *type = atype;
+ return 0;
+ }
}
return EINVAL;
}
@@ -776,7 +808,7 @@
{
if (attr && type >= PTHREAD_MUTEX_NORMAL &&
type <= PTHREAD_MUTEX_ERRORCHECK ) {
- *attr = type;
+ *attr = (*attr & ~MUTEXATTR_TYPE_MASK) | type;
return 0;
}
return EINVAL;
@@ -791,54 +823,70 @@
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
+ *attr &= ~MUTEXATTR_SHARED_MASK;
+ return 0;
+
case PTHREAD_PROCESS_SHARED:
/* our current implementation of pthread actually supports shared
* mutexes but won't cleanup if a process dies with the mutex held.
* Nevertheless, it's better than nothing. Shared mutexes are used
* by surfaceflinger and audioflinger.
*/
+ *attr |= MUTEXATTR_SHARED_MASK;
return 0;
}
-
- return ENOTSUP;
+ return EINVAL;
}
int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr, int *pshared)
{
- if (!attr)
+ if (!attr || !pshared)
return EINVAL;
- *pshared = PTHREAD_PROCESS_PRIVATE;
+ *pshared = (*attr & MUTEXATTR_SHARED_MASK) ? PTHREAD_PROCESS_SHARED
+ : PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_mutex_init(pthread_mutex_t *mutex,
const pthread_mutexattr_t *attr)
{
- if ( mutex ) {
- if (attr == NULL) {
- mutex->value = MUTEX_TYPE_NORMAL;
- return 0;
- }
- switch ( *attr ) {
- case PTHREAD_MUTEX_NORMAL:
- mutex->value = MUTEX_TYPE_NORMAL;
- return 0;
+ int value = 0;
- case PTHREAD_MUTEX_RECURSIVE:
- mutex->value = MUTEX_TYPE_RECURSIVE;
- return 0;
+ if (mutex == NULL)
+ return EINVAL;
- case PTHREAD_MUTEX_ERRORCHECK:
- mutex->value = MUTEX_TYPE_ERRORCHECK;
- return 0;
- }
+ if (__likely(attr == NULL)) {
+ mutex->value = MUTEX_TYPE_NORMAL;
+ return 0;
}
- return EINVAL;
+
+ if ((*attr & MUTEXATTR_SHARED_MASK) != 0)
+ value |= MUTEX_SHARED_MASK;
+
+ switch (*attr & MUTEXATTR_TYPE_MASK) {
+ case PTHREAD_MUTEX_NORMAL:
+ value |= MUTEX_TYPE_NORMAL;
+ break;
+ case PTHREAD_MUTEX_RECURSIVE:
+ value |= MUTEX_TYPE_RECURSIVE;
+ break;
+ case PTHREAD_MUTEX_ERRORCHECK:
+ value |= MUTEX_TYPE_ERRORCHECK;
+ break;
+ default:
+ return EINVAL;
+ }
+
+ mutex->value = value;
+ return 0;
}
int pthread_mutex_destroy(pthread_mutex_t *mutex)
{
+ if (__unlikely(mutex == NULL))
+ return EINVAL;
+
mutex->value = 0xdead10cc;
return 0;
}
@@ -859,13 +907,15 @@
static __inline__ void
_normal_lock(pthread_mutex_t* mutex)
{
+ /* We need to preserve the shared flag during operations */
+ int shared = mutex->value & MUTEX_SHARED_MASK;
/*
* The common case is an unlocked mutex, so we begin by trying to
* change the lock's state from 0 to 1. __atomic_cmpxchg() returns 0
* if it made the swap successfully. If the result is nonzero, this
* lock is already held by another thread.
*/
- if (__atomic_cmpxchg(0, 1, &mutex->value ) != 0) {
+ if (__atomic_cmpxchg(shared|0, shared|1, &mutex->value ) != 0) {
/*
* We want to go to sleep until the mutex is available, which
* requires promoting it to state 2. We need to swap in the new
@@ -882,8 +932,10 @@
* that the mutex is in state 2 when we go to sleep on it, which
* guarantees a wake-up call.
*/
- while (__atomic_swap(2, &mutex->value ) != 0)
- __futex_wait(&mutex->value, 2, 0);
+ int wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
+
+ while (__atomic_swap(shared|2, &mutex->value ) != (shared|0))
+ __futex_syscall4(&mutex->value, wait_op, shared|2, 0);
}
}
@@ -894,12 +946,16 @@
static __inline__ void
_normal_unlock(pthread_mutex_t* mutex)
{
+ /* We need to preserve the shared flag during operations */
+ int shared = mutex->value & MUTEX_SHARED_MASK;
+
/*
- * The mutex value will be 1 or (rarely) 2. We use an atomic decrement
+ * The mutex state will be 1 or (rarely) 2. We use an atomic decrement
* to release the lock. __atomic_dec() returns the previous value;
* if it wasn't 1 we have to do some additional work.
*/
- if (__atomic_dec(&mutex->value) != 1) {
+ if (__atomic_dec(&mutex->value) != (shared|1)) {
+ int wake_op = shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE;
/*
* Start by releasing the lock. The decrement changed it from
* "contended lock" to "uncontended lock", which means we still
@@ -914,7 +970,7 @@
* _normal_lock(), because the __futex_wait() call there will
* return immediately if the mutex value isn't 2.
*/
- mutex->value = 0;
+ mutex->value = shared;
/*
* Wake up one waiting thread. We don't know which thread will be
@@ -937,7 +993,7 @@
* Either way we have correct behavior and nobody is orphaned on
* the wait queue.
*/
- __futex_wake(&mutex->value, 1);
+ __futex_syscall3(&mutex->value, wake_op, 1);
}
}
@@ -946,26 +1002,24 @@
static void
_recursive_lock(void)
{
- _normal_lock( &__recursive_lock);
+ _normal_lock(&__recursive_lock);
}
static void
_recursive_unlock(void)
{
- _normal_unlock( &__recursive_lock );
+ _normal_unlock(&__recursive_lock );
}
-#define __likely(cond) __builtin_expect(!!(cond), 1)
-#define __unlikely(cond) __builtin_expect(!!(cond), 0)
-
int pthread_mutex_lock(pthread_mutex_t *mutex)
{
- int mtype, tid, new_lock_type;
+ int mtype, tid, new_lock_type, shared, wait_op;
if (__unlikely(mutex == NULL))
return EINVAL;
mtype = (mutex->value & MUTEX_TYPE_MASK);
+ shared = (mutex->value & MUTEX_SHARED_MASK);
/* Handle normal case first */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) ) {
@@ -1003,6 +1057,10 @@
*/
new_lock_type = 1;
+ /* compute futex wait opcode and restore shared flag in mtype */
+ wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
+ mtype |= shared;
+
for (;;) {
int oldv;
@@ -1027,7 +1085,7 @@
*/
new_lock_type = 2;
- __futex_wait( &mutex->value, oldv, 0 );
+ __futex_syscall4(&mutex->value, wait_op, oldv, NULL);
}
return 0;
}
@@ -1035,12 +1093,13 @@
int pthread_mutex_unlock(pthread_mutex_t *mutex)
{
- int mtype, tid, oldv;
+ int mtype, tid, oldv, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
- mtype = (mutex->value & MUTEX_TYPE_MASK);
+ mtype = (mutex->value & MUTEX_TYPE_MASK);
+ shared = (mutex->value & MUTEX_SHARED_MASK);
/* Handle common case first */
if (__likely(mtype == MUTEX_TYPE_NORMAL)) {
@@ -1060,31 +1119,33 @@
mutex->value = oldv - (1 << MUTEX_COUNTER_SHIFT);
oldv = 0;
} else {
- mutex->value = mtype;
+ mutex->value = shared | mtype;
}
_recursive_unlock();
/* Wake one waiting thread, if any */
- if ((oldv & 3) == 2)
- __futex_wake( &mutex->value, 1 );
-
+ if ((oldv & 3) == 2) {
+ int wake_op = shared ? FUTEX_WAIT_PRIVATE : FUTEX_WAIT;
+ __futex_syscall3(&mutex->value, wake_op, 1);
+ }
return 0;
}
int pthread_mutex_trylock(pthread_mutex_t *mutex)
{
- int mtype, tid, oldv;
+ int mtype, tid, oldv, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
- mtype = (mutex->value & MUTEX_TYPE_MASK);
+ mtype = (mutex->value & MUTEX_TYPE_MASK);
+ shared = (mutex->value & MUTEX_SHARED_MASK);
/* Handle common case first */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
- if (__atomic_cmpxchg(0, 1, &mutex->value) == 0)
+ if (__atomic_cmpxchg(shared|0, shared|1, &mutex->value) == 0)
return 0;
return EBUSY;
@@ -1109,6 +1170,9 @@
return 0;
}
+ /* Restore sharing bit in mtype */
+ mtype |= shared;
+
/* Try to lock it, just once. */
_recursive_lock();
oldv = mutex->value;
@@ -1162,7 +1226,7 @@
clockid_t clock = CLOCK_MONOTONIC;
struct timespec abstime;
struct timespec ts;
- int mtype, tid, oldv, new_lock_type;
+ int mtype, tid, oldv, new_lock_type, shared, wait_op;
/* compute absolute expiration time */
__timespec_to_relative_msec(&abstime, msecs, clock);
@@ -1170,21 +1234,24 @@
if (__unlikely(mutex == NULL))
return EINVAL;
- mtype = (mutex->value & MUTEX_TYPE_MASK);
+ mtype = (mutex->value & MUTEX_TYPE_MASK);
+ shared = (mutex->value & MUTEX_SHARED_MASK);
/* Handle common case first */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
+ int wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
+
/* fast path for unconteded lock */
- if (__atomic_cmpxchg(0, 1, &mutex->value) == 0)
+ if (__atomic_cmpxchg(shared|0, shared|1, &mutex->value) == 0)
return 0;
/* loop while needed */
- while (__atomic_swap(2, &mutex->value) != 0) {
+ while (__atomic_swap(shared|2, &mutex->value) != (shared|0)) {
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
- __futex_wait(&mutex->value, 2, &ts);
+ __futex_syscall4(&mutex->value, wait_op, shared|2, &ts);
}
return 0;
}
@@ -1215,6 +1282,10 @@
*/
new_lock_type = 1;
+ /* Compute wait op and restore sharing bit in mtype */
+ wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
+ mtype |= shared;
+
for (;;) {
int oldv;
struct timespec ts;
@@ -1243,7 +1314,7 @@
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
- __futex_wait( &mutex->value, oldv, &ts );
+ __futex_syscall4(&mutex->value, wait_op, oldv, &ts);
}
return 0;
}
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index ec147c2..08b2009 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -83,6 +83,11 @@
- <pthread.h>: Add pthread_condattr_init/destroy/setpshared/getpshared functions
to enable proper shared conditional variable initialization.
+ Modify the pthread_mutex_t implementation to use private futexes for
+ performance reasons. Mutexes are no longer shareable between processes
+ by default anymore, unless you use PTHREAD_PROCESS_SHARED with
+ pthread_mutexattr_setpshared().
+
XXX: The implementation still always uses shared condvars, independent
of the flags being selected. This will change in a later commit.
