jyapayne/musl
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

new internal locking primitive; drop spinlocks

Browse source 
we use priority inheritance futexes if possible so that the library
cannot hit internal priority inversion deadlocks in the presence of
realtime priority scheduling (full support to be added later).
This commit is contained in:
Rich Felker 2012-04-24 06:36:50 -04:00
commit f34d0ea511
2 changed files with 29 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

33
src/thread/__lock.c
View file

@ -1,11 +1,32 @@
#include "pthread_impl.h"
void __lock_2(volatile int *l)
{
if (!__syscall(SYS_futex, l, FUTEX_LOCK_PI, 0, 0))
return;
int old, tid = __pthread_self()->tid;
while ((old = a_cas(l, 0, tid))) {
a_cas(l, old, old|INT_MIN);
__syscall(SYS_futex, l, FUTEX_WAIT, old|INT_MIN, 0);
}
}
void __lock(volatile int *l)
{
int spins=10000;
/* Do not use futexes because we insist that unlocking is a simple
* assignment to optimize non-pathological code with no contention. */
while (a_swap(l, 1))
if (spins) spins--, a_spin();
else __syscall(SYS_sched_yield);
if (a_cas(l, 0, __pthread_self()->tid)) __lock_2(l);
}
void __unlock_2(volatile int *l)
{
if (__syscall(SYS_futex, l, FUTEX_UNLOCK_PI)) {
*l = 0;
__syscall(SYS_futex, l, FUTEX_WAKE, 1);
}
}
void __unlock(volatile int *l)
{
int old = *l;
if (!(old & INT_MIN) && a_cas(l, old, 0)==old) return;
__unlock_2(l);
}