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Remove the DCB write queue locking

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Since only one thread can append to the DCBs write queue at a time, there
is no need to lock it.
This commit is contained in:
Markus Makela 2016-10-26 23:42:33 +03:00
parent 076b810c1e
commit 68d3fc1092
2 changed files with 5 additions and 21 deletions
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24
server/core/dcb.c
View File

@ -1122,19 +1122,14 @@ dcb_basic_read_SSL(DCB *dcb, int *nsingleread)
*nsingleread = -1;
return NULL;
}
spinlock_acquire(&dcb->writeqlock);
/* If we were in a retry situation, need to clear flag and attempt write */
if (dcb->ssl_read_want_write || dcb->ssl_read_want_read)
{
dcb->ssl_read_want_write = false;
dcb->ssl_read_want_read = false;
spinlock_release(&dcb->writeqlock);
dcb_drain_writeq(dcb);
}
else
{
spinlock_release(&dcb->writeqlock);
}
break;
case SSL_ERROR_ZERO_RETURN:
@ -1153,10 +1148,8 @@ dcb_basic_read_SSL(DCB *dcb, int *nsingleread)
pthread_self(),
__func__
);
spinlock_acquire(&dcb->writeqlock);
dcb->ssl_read_want_write = false;
dcb->ssl_read_want_read = true;
spinlock_release(&dcb->writeqlock);
*nsingleread = 0;
break;
@ -1166,10 +1159,8 @@ dcb_basic_read_SSL(DCB *dcb, int *nsingleread)
pthread_self(),
__func__
);
spinlock_acquire(&dcb->writeqlock);
dcb->ssl_read_want_write = true;
dcb->ssl_read_want_read = false;
spinlock_release(&dcb->writeqlock);
*nsingleread = 0;
break;
@ -1253,7 +1244,6 @@ dcb_write(DCB *dcb, GWBUF *queue)
return 0;
}
spinlock_acquire(&dcb->writeqlock);
empty_queue = (dcb->writeq == NULL);
/*
* Add our data to the write queue. If the queue already had data,
@ -1261,10 +1251,10 @@ dcb_write(DCB *dcb, GWBUF *queue)
* If it did not already have data, we call the drain write queue
* function immediately to attempt to write the data.
*/
atomic_add(&dcb->writeqlen, gwbuf_length(queue));
dcb->writeqlen += gwbuf_length(queue);
dcb->writeq = gwbuf_append(dcb->writeq, queue);
spinlock_release(&dcb->writeqlock);
dcb->stats.n_buffered++;
MXS_DEBUG("%lu [dcb_write] Append to writequeue. %d writes "
"buffered for dcb %p in state %s fd %d",
pthread_self(),
@ -1494,7 +1484,6 @@ dcb_drain_writeq(DCB *dcb)
*/
if (stop_writing)
{
spinlock_acquire(&dcb->writeqlock);
dcb->writeq = gwbuf_append(local_writeq, dcb->writeq);
if (dcb->drain_called_while_busy)
@ -1502,13 +1491,11 @@ dcb_drain_writeq(DCB *dcb)
local_writeq = dcb->writeq;
dcb->writeq = NULL;
dcb->drain_called_while_busy = false;
spinlock_release(&dcb->writeqlock);
continue;
}
else
{
dcb->draining_flag = false;
spinlock_release(&dcb->writeqlock);
goto wrap_up;
}
}
@ -1532,7 +1519,7 @@ wrap_up:
*/
if (total_written)
{
atomic_add(&dcb->writeqlen, -total_written);
dcb->writeqlen -= total_written;
/* Check if the draining has taken us from above water to below water */
if (above_water && dcb->writeqlen < dcb->low_water)
@ -1566,7 +1553,6 @@ static GWBUF *
dcb_grab_writeq(DCB *dcb, bool first_time)
{
GWBUF *local_writeq = NULL;
spinlock_acquire(&dcb->writeqlock);
if (first_time && dcb->ssl_read_want_write)
{
@ -1583,7 +1569,7 @@ dcb_grab_writeq(DCB *dcb, bool first_time)
dcb->draining_flag = local_writeq ? true : false;
dcb->writeq = NULL;
}
spinlock_release(&dcb->writeqlock);
return local_writeq;
}

2
server/modules/protocol/MySQL/MySQLBackend/mysql_backend.c
View File

@ -884,13 +884,11 @@ static int gw_write_backend_event(DCB *dcb)
uint8_t* data = NULL;
bool com_quit = false;
spinlock_acquire(&dcb->writeqlock);
if (dcb->writeq)
{
data = (uint8_t *) GWBUF_DATA(dcb->writeq);
com_quit = MYSQL_IS_COM_QUIT(data);
}
spinlock_release(&dcb->writeqlock);
if (data)
{