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authorRich Felker <dalias@aerifal.cx>2011-09-27 13:50:29 -0400
committerRich Felker <dalias@aerifal.cx>2011-09-27 13:50:29 -0400
commit60164570111873175111cf8a5b973375e492eee9 (patch)
tree1557931c4e0bacd2be217965be08031d5e3a4e51 /src
parent3f39c9b3130cd6c142d358159879b799370a6663 (diff)
downloadmusl-60164570111873175111cf8a5b973375e492eee9.tar.gz
process-shared barrier support, based on discussion with bdonlan
this implementation is rather heavy-weight, but it's the first solution i've found that's actually correct. all waiters actually wait twice at the barrier so that they can synchronize exit, and they hold a "vm lock" that prevents changes to virtual memory mappings (and blocks pthread_barrier_destroy) until all waiters are finished inspecting the barrier. thus, it is safe for any thread to destroy and/or unmap the barrier's memory as soon as pthread_barrier_wait returns, without further synchronization.
Diffstat (limited to 'src')
-rw-r--r--src/internal/pthread_impl.h8
-rw-r--r--src/mman/mmap.c13
-rw-r--r--src/mman/munmap.c11
-rw-r--r--src/thread/pthread_barrier_destroy.c6
-rw-r--r--src/thread/pthread_barrier_init.c4
-rw-r--r--src/thread/pthread_barrier_wait.c74
-rw-r--r--src/thread/pthread_barrierattr_setpshared.c2
7 files changed, 102 insertions, 16 deletions
diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index bbb4502f..82d62426 100644
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -73,10 +73,12 @@ struct __timer {
#define _c_waiters2 __u.__i[7]
#define _rw_lock __u.__i[0]
#define _rw_waiters __u.__i[1]
-#define _b_inst __u.__p[0]
+#define _b_lock __u.__i[0]
+#define _b_waiters __u.__i[1]
#define _b_limit __u.__i[2]
-#define _b_lock __u.__i[3]
-#define _b_waiters __u.__i[4]
+#define _b_count __u.__i[3]
+#define _b_seq __u.__i[4]
+#define _b_inst __u.__p[4]
#include "pthread_arch.h"
diff --git a/src/mman/mmap.c b/src/mman/mmap.c
index 883acb28..fd2bb07e 100644
--- a/src/mman/mmap.c
+++ b/src/mman/mmap.c
@@ -5,16 +5,25 @@
#include "syscall.h"
#include "libc.h"
+static void dummy1(int x) { }
+static void dummy0(void) { }
+weak_alias(dummy1, __vm_lock);
+weak_alias(dummy0, __vm_unlock);
+
void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off)
{
+ void *ret;
if (sizeof(off_t) > sizeof(long))
if (((long)off & 0xfff) | ((long)((unsigned long long)off>>(12 + 8*(sizeof(off_t)-sizeof(long))))))
start = (void *)-1;
+ if (flags & MAP_FIXED) __vm_lock(-1);
#ifdef SYS_mmap2
- return (void *)syscall(SYS_mmap2, start, len, prot, flags, fd, off>>12);
+ ret = (void *)syscall(SYS_mmap2, start, len, prot, flags, fd, off>>12);
#else
- return (void *)syscall(SYS_mmap, start, len, prot, flags, fd, off);
+ ret = (void *)syscall(SYS_mmap, start, len, prot, flags, fd, off);
#endif
+ if (flags & MAP_FIXED) __vm_unlock();
+ return ret;
}
weak_alias(__mmap, mmap);
diff --git a/src/mman/munmap.c b/src/mman/munmap.c
index ab7da9e2..91aefd40 100644
--- a/src/mman/munmap.c
+++ b/src/mman/munmap.c
@@ -3,9 +3,18 @@
#include "syscall.h"
#include "libc.h"
+static void dummy1(int x) { }
+static void dummy0(void) { }
+weak_alias(dummy1, __vm_lock);
+weak_alias(dummy0, __vm_unlock);
+
int __munmap(void *start, size_t len)
{
- return syscall(SYS_munmap, start, len);
+ int ret;
+ __vm_lock(-1);
+ ret = syscall(SYS_munmap, start, len);
+ __vm_unlock();
+ return ret;
}
weak_alias(__munmap, munmap);
diff --git a/src/thread/pthread_barrier_destroy.c b/src/thread/pthread_barrier_destroy.c
index 2898c41a..f82664d5 100644
--- a/src/thread/pthread_barrier_destroy.c
+++ b/src/thread/pthread_barrier_destroy.c
@@ -1,6 +1,12 @@
#include "pthread_impl.h"
+void __vm_lock(int), __vm_unlock(void);
+
int pthread_barrier_destroy(pthread_barrier_t *b)
{
+ if (b->_b_limit < 0) {
+ __vm_lock(-1);
+ __vm_unlock();
+ }
return 0;
}
diff --git a/src/thread/pthread_barrier_init.c b/src/thread/pthread_barrier_init.c
index 736d1014..ccaab4eb 100644
--- a/src/thread/pthread_barrier_init.c
+++ b/src/thread/pthread_barrier_init.c
@@ -2,7 +2,7 @@
int pthread_barrier_init(pthread_barrier_t *b, const pthread_barrierattr_t *a, unsigned count)
{
- if (!count) return EINVAL;
- *b = (pthread_barrier_t){ ._b_limit = count-1 };
+ if (count-1 > INT_MAX-1) return EINVAL;
+ *b = (pthread_barrier_t){ ._b_limit = count-1 | (a?*a:0) };
return 0;
}
diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index aed1adc8..db432ba3 100644
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,5 +1,62 @@
#include "pthread_impl.h"
+static int vmlock[2];
+
+void __vm_lock(int inc)
+{
+ for (;;) {
+ int v = vmlock[0];
+ if (inc*v < 0) __wait(vmlock, vmlock+1, v, 1);
+ else if (a_cas(vmlock, v, v+inc)==v) break;
+ }
+}
+
+void __vm_unlock(void)
+{
+ if (vmlock[0]>0) a_dec(vmlock);
+ else a_inc(vmlock);
+ if (vmlock[1]) __wake(vmlock, 1, 1);
+}
+
+static int pshared_barrier_wait(pthread_barrier_t *b)
+{
+ int limit = (b->_b_limit & INT_MAX) + 1;
+ int seq;
+ int ret = 0;
+
+ if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+ while (a_swap(&b->_b_lock, 1))
+ __wait(&b->_b_lock, &b->_b_waiters, 1, 0);
+
+ seq = b->_b_seq;
+
+ if (++b->_b_count == limit) {
+ ret = PTHREAD_BARRIER_SERIAL_THREAD;
+ b->_b_seq++;
+ __wake(&b->_b_seq, -1, 0);
+ } else {
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ __wait(&b->_b_seq, 0, seq, 0);
+ }
+
+ __vm_lock(+1);
+
+ if (a_fetch_add(&b->_b_count, -1)==1) {
+ b->_b_seq++;
+ __wake(&b->_b_seq, -1, 0);
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ } else {
+ __wait(&b->_b_seq, 0, seq+1, 0);
+ }
+
+ __vm_unlock();
+
+ return 0;
+}
+
struct instance
{
int count;
@@ -16,9 +73,12 @@ int pthread_barrier_wait(pthread_barrier_t *b)
/* Trivial case: count was set at 1 */
if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+ /* Process-shared barriers require a separate, inefficient wait */
+ if (limit < 0) return pshared_barrier_wait(b);
+
/* Otherwise we need a lock on the barrier object */
while (a_swap(&b->_b_lock, 1))
- __wait(&b->_b_lock, &b->_b_waiters, 1, 0);
+ __wait(&b->_b_lock, &b->_b_waiters, 1, 1);
inst = b->_b_inst;
/* First thread to enter the barrier becomes the "instance owner" */
@@ -27,7 +87,7 @@ int pthread_barrier_wait(pthread_barrier_t *b)
int spins = 10000;
b->_b_inst = inst = &new_inst;
a_store(&b->_b_lock, 0);
- if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
while (spins-- && !inst->finished)
a_spin();
a_inc(&inst->finished);
@@ -40,19 +100,19 @@ int pthread_barrier_wait(pthread_barrier_t *b)
if (++inst->count == limit) {
b->_b_inst = 0;
a_store(&b->_b_lock, 0);
- if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
a_store(&inst->last, 1);
if (inst->waiters)
- __wake(&inst->last, -1, 0);
+ __wake(&inst->last, -1, 1);
} else {
a_store(&b->_b_lock, 0);
- if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
- __wait(&inst->last, &inst->waiters, 0, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
+ __wait(&inst->last, &inst->waiters, 0, 1);
}
/* Last thread to exit the barrier wakes the instance owner */
if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
- __wake(&inst->finished, 1, 0);
+ __wake(&inst->finished, 1, 1);
return 0;
}
diff --git a/src/thread/pthread_barrierattr_setpshared.c b/src/thread/pthread_barrierattr_setpshared.c
index d6c7f9a3..1edc95dc 100644
--- a/src/thread/pthread_barrierattr_setpshared.c
+++ b/src/thread/pthread_barrierattr_setpshared.c
@@ -2,6 +2,6 @@
int pthread_barrierattr_setpshared(pthread_barrierattr_t *a, int pshared)
{
- *a = !!pshared;
+ *a = pshared ? INT_MIN : 0;
return 0;
}