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体验新版 GitCode,发现更多精彩内容 >>
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d5f7d2c6
编写于
8月 06, 2003
作者:
T
Tom Lane
浏览文件
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电子邮件补丁
差异文件
Adopt a random backoff algorithm for sleep delays when waiting for a
spinlock. Per recent pghackers discussion.
上级
a6672880
变更
1
显示空白变更内容
内联
并排
Showing
1 changed file
with
53 addition
and
18 deletion
+53
-18
src/backend/storage/lmgr/s_lock.c
src/backend/storage/lmgr/s_lock.c
+53
-18
未找到文件。
src/backend/storage/lmgr/s_lock.c
浏览文件 @
d5f7d2c6
...
...
@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/s_lock.c,v 1.1
4 2003/08/04 15:28:3
3 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/s_lock.c,v 1.1
5 2003/08/06 16:43:4
3 tgl Exp $
*
*-------------------------------------------------------------------------
*/
...
...
@@ -31,7 +31,7 @@ s_lock_stuck(volatile slock_t *lock, const char *file, int line)
fprintf
(
stderr
,
"
\n
Stuck spinlock (%p) detected at %s:%d.
\n
"
,
lock
,
file
,
line
);
abort
(
);
exit
(
1
);
#else
elog
(
PANIC
,
"stuck spinlock (%p) detected at %s:%d"
,
lock
,
file
,
line
);
...
...
@@ -45,35 +45,68 @@ s_lock_stuck(volatile slock_t *lock, const char *file, int line)
void
s_lock
(
volatile
slock_t
*
lock
,
const
char
*
file
,
int
line
)
{
unsigned
spins
=
0
;
unsigned
delays
=
0
;
struct
timeval
delay
;
/*
* We loop tightly for awhile, then delay using select() and try
* again. Preferably, "awhile" should be a small multiple of the
* maximum time we expect a spinlock to be held. 100 iterations seems
* about right.
* about right. In most multi-CPU scenarios, the spinlock is probably
* held by a process on another CPU and will be released before we
* finish 100 iterations. However, on a uniprocessor, the tight loop
* is just a waste of cycles, so don't iterate thousands of times.
*
* Once we do decide to block, we use randomly increasing select() delays.
* The first delay is 10 msec, then the delay randomly increases to about
* one second, after which we reset to 10 msec and start again. The idea
* here is that in the presence of heavy contention we need to increase
* the delay, else the spinlock holder may never get to run and release
* the lock. (Consider situation where spinlock holder has been nice'd
* down in priority by the scheduler --- it will not get scheduled until
* all would-be acquirers are sleeping, so if we always use a 10-msec
* sleep, there is a real possibility of starvation.) But we can't just
* clamp the delay to an upper bound, else it would take a long time to
* make a reasonable number of tries.
*
* We use a 10 millisec select delay because that is the lower limit on
* many platforms. The timeout is figured on this delay only, and so
* the nominal 1 minute is a lower bound.
* We time out and declare error after NUM_DELAYS delays (thus, exactly
* that many tries). With the given settings, this will usually take
* 3 or so minutes. It seems better to fix the total number of tries (and
* thus the probability of unintended failure) than to fix the total time
* spent.
*
* The select() delays are measured in centiseconds (0.01 sec) because
* 10 msec is a common resolution limit at the OS level.
*/
#define SPINS_PER_DELAY 100
#define DELAY_MSEC 10
#define TIMEOUT_MSEC (60 * 1000)
#define NUM_DELAYS 1000
#define MIN_DELAY_CSEC 1
#define MAX_DELAY_CSEC 100
int
spins
=
0
;
int
delays
=
0
;
int
cur_delay
=
MIN_DELAY_CSEC
;
struct
timeval
delay
;
while
(
TAS
(
lock
))
{
if
(
++
spins
>
SPINS_PER_DELAY
)
{
if
(
++
delays
>
(
TIMEOUT_MSEC
/
DELAY_MSEC
)
)
if
(
++
delays
>
NUM_DELAYS
)
s_lock_stuck
(
lock
,
file
,
line
);
delay
.
tv_sec
=
0
;
delay
.
tv_usec
=
DELAY_MSEC
*
1
000
;
delay
.
tv_sec
=
cur_delay
/
10
0
;
delay
.
tv_usec
=
(
cur_delay
%
100
)
*
10
000
;
(
void
)
select
(
0
,
NULL
,
NULL
,
NULL
,
&
delay
);
#if defined(S_LOCK_TEST)
fprintf
(
stdout
,
"*"
);
fflush
(
stdout
);
#endif
/* increase delay by a random fraction between 1X and 2X */
cur_delay
+=
(
int
)
(
cur_delay
*
(((
double
)
random
())
/
((
double
)
MAX_RANDOM_VALUE
))
+
0
.
5
);
/* wrap back to minimum delay when max is exceeded */
if
(
cur_delay
>
MAX_DELAY_CSEC
)
cur_delay
=
MIN_DELAY_CSEC
;
spins
=
0
;
}
}
...
...
@@ -217,6 +250,8 @@ volatile slock_t test_lock;
int
main
()
{
srandom
((
unsigned
int
)
time
(
NULL
));
S_INIT_LOCK
(
&
test_lock
);
if
(
!
S_LOCK_FREE
(
&
test_lock
))
...
...
@@ -249,9 +284,9 @@ main()
return
1
;
}
printf
(
"S_LOCK_TEST: this will
hang for a minute or so and then abort
\n
"
);
printf
(
"
with a 'stuck spinlock' message if S_LOCK()
\n
"
);
printf
(
" and TAS() are working.
\n
"
);
printf
(
"S_LOCK_TEST: this will
print %d stars and then
\n
"
,
NUM_DELAYS
);
printf
(
"
exit with a 'stuck spinlock' message
\n
"
);
printf
(
"
if S_LOCK()
and TAS() are working.
\n
"
);
fflush
(
stdout
);
s_lock
(
&
test_lock
,
__FILE__
,
__LINE__
);
...
...
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