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cwfs: use atomic compare and swap to avoid semacquire() syscalls in new queue implementation

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This commit is contained in:
cinap_lenrek 2013-08-07 01:32:11 +02:00
parent 2c8f291db2
commit 3663ffeefa
1 changed files with 11 additions and 2 deletions
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13
sys/src/cmd/cwfs/sub.c
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@ -917,12 +917,17 @@ hexdump(void *a, int n)
fprint(2, "%s\n", s1);
}
extern int cas(long *p, long ov, long nv);
void*
fs_recv(Queue *q, int)
{
void *a;
long v;
semacquire(&q->count, 1);
v = q->count;
if(v == 0 || cas(&q->count, v, v-1) == 0)
semacquire(&q->count, 1);
lock(&q->rl);
a = *q->rp;
if(++q->rp >= &q->args[q->size])
@ -935,7 +940,11 @@ fs_recv(Queue *q, int)
void
fs_send(Queue *q, void *a)
{
semacquire(&q->avail, 1);
long v;
v = q->avail;
if(v == 0 || cas(&q->avail, v, v-1) == 0)
semacquire(&q->avail, 1);
lock(&q->wl);
*q->wp = a;
if(++q->wp >= &q->args[q->size])