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runtime: respect timeout in semasleep on Darwin

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semasleep on Darwin was refactored in https://golang.org/cl/118736 to
use the pthread_cond_timedwait function from libc. The new code
incorrectly assumed that pthread_cond_timedwait took a timeout relative
to the current time, when it in fact it takes a timeout specified in
absolute time. semasleep thus specified a timeout well in the past,
causing it to immediately exceed the timeout and spin hot. This was the
source of a large performance hit to CockroachDB (#26019).

Adjust semasleep to instead call pthread_cond_timedwait_relative_np,
which properly interprets its timeout parameter as relative to the
current time.

pthread_cond_timedwait_relative_np is non-portable, but using
pthread_cond_timedwait correctly would require two calls to
gettimeofday: one in the runtime package to convert the relative timeout
to absolute time, then another in the pthread library to convert back to
a relative offset [0], as the Darwin kernel expects a relative offset.

[0]: https://opensource.apple.com/source/libpthread/libpthread-301.30.1/src/pthread_cond.c.auto.html

Fix #26019.

Change-Id: I1a8c2429f79513b43d2b256365cd9166d235af8b
Reviewed-on: https://go-review.googlesource.com/120635
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Nikhil Benesch 2018-06-23 01:15:19 -04:00 committed by Josh Bleecher Snyder
parent 291e57f057
commit 6fdbed0543
6 changed files with 13 additions and 13 deletions
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2
src/runtime/os_darwin.go
View File

@ -45,7 +45,7 @@ func semasleep(ns int64) int32 {
if ns >= 0 {
var t timespec
t.set_nsec(ns)
err := pthread_cond_timedwait(&mp.cond, &mp.mutex, &t)
err := pthread_cond_timedwait_relative_np(&mp.cond, &mp.mutex, &t)
if err == _ETIMEDOUT {
pthread_mutex_unlock(&mp.mutex)
return -1

8
src/runtime/sys_darwin.go
View File

@ -287,10 +287,10 @@ func pthread_cond_wait_trampoline()
//go:nosplit
//go:cgo_unsafe_args
func pthread_cond_timedwait(c *pthreadcond, m *pthreadmutex, t *timespec) int32 {
return libcCall(unsafe.Pointer(funcPC(pthread_cond_timedwait_trampoline)), unsafe.Pointer(&c))
func pthread_cond_timedwait_relative_np(c *pthreadcond, m *pthreadmutex, t *timespec) int32 {
return libcCall(unsafe.Pointer(funcPC(pthread_cond_timedwait_relative_np_trampoline)), unsafe.Pointer(&c))
}
func pthread_cond_timedwait_trampoline()
func pthread_cond_timedwait_relative_np_trampoline()
//go:nosplit
//go:cgo_unsafe_args
@ -348,7 +348,7 @@ func closeonexec(fd int32) {
//go:cgo_import_dynamic libc_pthread_mutex_unlock pthread_mutex_unlock "/usr/lib/libSystem.B.dylib"
//go:cgo_import_dynamic libc_pthread_cond_init pthread_cond_init "/usr/lib/libSystem.B.dylib"
//go:cgo_import_dynamic libc_pthread_cond_wait pthread_cond_wait "/usr/lib/libSystem.B.dylib"
//go:cgo_import_dynamic libc_pthread_cond_timedwait pthread_cond_timedwait "/usr/lib/libSystem.B.dylib"
//go:cgo_import_dynamic libc_pthread_cond_timedwait_relative_np pthread_cond_timedwait_relative_np "/usr/lib/libSystem.B.dylib"
//go:cgo_import_dynamic libc_pthread_cond_signal pthread_cond_signal "/usr/lib/libSystem.B.dylib"
// Magic incantation to get libSystem actually dynamically linked.

4
src/runtime/sys_darwin_386.s
View File

@ -595,7 +595,7 @@ TEXT runtime·pthread_cond_wait_trampoline(SB),NOSPLIT,$0
POPL BP
RET
TEXT runtime·pthread_cond_timedwait_trampoline(SB),NOSPLIT,$0
TEXT runtime·pthread_cond_timedwait_relative_np_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $24, SP
@ -606,7 +606,7 @@ TEXT runtime·pthread_cond_timedwait_trampoline(SB),NOSPLIT,$0
MOVL AX, 4(SP)
MOVL 8(CX), AX // arg 3 timeout
MOVL AX, 8(SP)
CALL libc_pthread_cond_timedwait(SB)
CALL libc_pthread_cond_timedwait_relative_np(SB)
MOVL BP, SP
POPL BP
RET

4
src/runtime/sys_darwin_amd64.s
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@ -447,13 +447,13 @@ TEXT runtime·pthread_cond_wait_trampoline(SB),NOSPLIT,$0
POPQ BP
RET
TEXT runtime·pthread_cond_timedwait_trampoline(SB),NOSPLIT,$0
TEXT runtime·pthread_cond_timedwait_relative_np_trampoline(SB),NOSPLIT,$0
PUSHQ BP
MOVQ SP, BP
MOVQ 8(DI), SI // arg 2 mutex
MOVQ 16(DI), DX // arg 3 timeout
MOVQ 0(DI), DI // arg 1 cond
CALL libc_pthread_cond_timedwait(SB)
CALL libc_pthread_cond_timedwait_relative_np(SB)
POPQ BP
RET

4
src/runtime/sys_darwin_arm.s
View File

@ -368,11 +368,11 @@ TEXT runtime·pthread_cond_wait_trampoline(SB),NOSPLIT,$0
BL libc_pthread_cond_wait(SB)
RET
TEXT runtime·pthread_cond_timedwait_trampoline(SB),NOSPLIT,$0
TEXT runtime·pthread_cond_timedwait_relative_np_trampoline(SB),NOSPLIT,$0
MOVW 4(R0), R1 // arg 2 mutex
MOVW 8(R0), R2 // arg 3 timeout
MOVW 0(R0), R0 // arg 1 cond
BL libc_pthread_cond_timedwait(SB)
BL libc_pthread_cond_timedwait_relative_np(SB)
RET
TEXT runtime·pthread_cond_signal_trampoline(SB),NOSPLIT,$0

4
src/runtime/sys_darwin_arm64.s
View File

@ -357,11 +357,11 @@ TEXT runtime·pthread_cond_wait_trampoline(SB),NOSPLIT,$0
BL libc_pthread_cond_wait(SB)
RET
TEXT runtime·pthread_cond_timedwait_trampoline(SB),NOSPLIT,$0
TEXT runtime·pthread_cond_timedwait_relative_np_trampoline(SB),NOSPLIT,$0
MOVD 8(R0), R1 // arg 2 mutex
MOVD 16(R0), R2 // arg 3 timeout
MOVD 0(R0), R0 // arg 1 cond
BL libc_pthread_cond_timedwait(SB)
BL libc_pthread_cond_timedwait_relative_np(SB)
RET
TEXT runtime·pthread_cond_signal_trampoline(SB),NOSPLIT,$0