commit 6be4a5eb4898c7b5e7557dda061cc09ba310698b [browse]
Author: Dmitri Shuralyov
Date: 2020-06-01 13:15:51 -04:00
[release-branch.go1.13] go1.13.12
Change-Id: I1989d7cab0bf75c4e42d1c48146be9131d2c105c
Reviewed-on: https://go-review.googlesource.com/c/go/+/235918
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
commit 90fe4a73fff10394097e21085a9c0c369c61b09a [browse]
Author: Robert Griesemer
Date: 2019-10-23 16:44:51 -07:00
[release-branch.go1.13] math/big: make Rat.Denom side-effect free
A Rat is represented via a quotient a/b where a and b are Int values.
To make it possible to use an uninitialized Rat value (with a and b
uninitialized and thus == 0), the implementation treats a 0 denominator
as 1.
Rat.Num and Rat.Denom return pointers to these values a and b. Because
b may be 0, Rat.Denom used to first initialize it to 1 and thus produce
an undesirable side-effect (by changing the Rat's denominator).
This CL changes Denom to return a new (not shared) *Int with value 1
in the rare case where the Rat was not initialized. This eliminates
the side effect and returns the correct denominator value.
While this is changing behavior of the API, the impact should now be
minor because together with (prior) CL https://golang.org/cl/202997,
which initializes Rats ASAP, Denom is unlikely used to access the
denominator of an uninitialized (and thus 0) Rat. Any operation that
will somehow set a Rat value will ensure that the denominator is not 0.
Fixes #36689.
For #33792.
For #3521.
Change-Id: I0bf15ac60513cf52162bfb62440817ba36f0c3fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/203059
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/233323
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
commit 7f1ef49347e6e1f5a51c9ca3e4f4f617c2317042 [browse]
Author: Robert Griesemer
Date: 2019-10-23 14:22:32 -07:00
[release-branch.go1.13] math/big: normalize unitialized denominators ASAP
A Rat is represented via a quotient a/b where a and b are Int values.
To make it possible to use an uninitialized Rat value (with a and b
uninitialized and thus == 0), the implementation treats a 0 denominator
as 1.
For each operation we check if the denominator is 0, and then treat
it as 1 (if necessary). Operations that create a new Rat result,
normalize that value such that a result denominator 1 is represened
as 0 again.
This CL changes this behavior slightly: 0 denominators are still
interpreted as 1, but whenever we (safely) can, we set an uninitialized
0 denominator to 1. This simplifies the code overall.
Also: Improved some doc strings.
Preparation for addressing issue #33792.
For #36689.
For #33792.
Change-Id: I3040587c8d0dad2e840022f96ca027d8470878a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/202997
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/233322
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
commit 444ad952c4dd346955362165aa20d0b4938ffcca [browse]
Author: Robert Griesemer
Date: 2019-10-15 13:44:22 -07:00
[release-branch.go1.13] math/big: make Rat accessors safe for concurrent use
Do not modify the underlying Rat denominator when calling
one of the accessors Float32, Float64; verify that we don't
modify the Rat denominator when calling Inv, Sign, IsInt, Num.
For #36689.
For #34919.
For #33792.
Change-Id: Ife6d1252373f493a597398ee51e7b5695b708df5
Reviewed-on: https://go-review.googlesource.com/c/go/+/201205
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/233321
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
commit 1a1178122f31bfe67534ec637883636755adbfbc [browse]
Author: Michael Pratt
Date: 2020-05-07 18:13:21 -04:00
[release-branch.go1.13] runtime: disable preemption in startTemplateThread
When a locked M wants to start a new M, it hands off to the template
thread to actually call clone and start the thread. The template thread
is lazily created the first time a thread is locked (or if cgo is in
use).
stoplockedm will release the P (_Pidle), then call handoffp to give the
P to another M. In the case of a pending STW, one of two things can
happen:
1. handoffp starts an M, which does acquirep followed by schedule, which
will finally enter _Pgcstop.
2. handoffp immediately enters _Pgcstop. This only occurs if the P has
no local work, GC work, and no spinning M is required.
If handoffp starts an M, and must create a new M to do so, then newm
will simply queue the M on newmHandoff for the template thread to do the
clone.
When a stop-the-world is required, stopTheWorldWithSema will start the
stop and then wait for all Ps to enter _Pgcstop. If the template thread
is not fully created because startTemplateThread gets stopped, then
another stoplockedm may queue an M that will never get created, and the
handoff P will never leave _Pidle. Thus stopTheWorldWithSema will wait
forever.
A sequence to trigger this hang when STW occurs can be visualized with
two threads:
T1 T2
------------------------------- -----------------------------
LockOSThread LockOSThread
haveTemplateThread == 0
startTemplateThread
haveTemplateThread = 1
newm haveTemplateThread == 1
preempt -> schedule g.m.lockedExt++
gcstopm -> _Pgcstop g.m.lockedg = ...
park g.lockedm = ...
return
... (any code)
preempt -> schedule
stoplockedm
releasep -> _Pidle
handoffp
startm (first 3 handoffp cases)
newm
g.m.lockedExt != 0
Add to newmHandoff, return
park
Note that the P in T2 is stuck sitting in _Pidle. Since the template
thread isn't running, the new M will not be started complete the
transition to _Pgcstop.
To resolve this, we disable preemption around the assignment of
haveTemplateThread and the creation of the template thread in order to
guarantee that if handTemplateThread is set then the template thread
will eventually exist, in the presence of stops.
For #38931
Fixes #38932
Change-Id: I50535fbbe2f328f47b18e24d9030136719274191
Reviewed-on: https://go-review.googlesource.com/c/go/+/232978
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
(cherry picked from commit 11b3730a02c93fd5745bfd977156541a9033759b)
Reviewed-on: https://go-review.googlesource.com/c/go/+/234888
Reviewed-by: Cherry Zhang <cherryyz@google.com>
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