Currently the GC coordinator enables GC assists at the same time it
enables background mark workers, after the concurrent scan phase is
done. However, this means a rapidly allocating mutator has the entire
scan phase during which to allocate beyond the heap trigger and
potentially beyond the heap goal with no back-pressure from assists.
This prevents the feedback system that's supposed to keep the heap
size under the heap goal from doing its job.

Fix this by enabling mutator assists during the scan phase. This is
safe because the write barrier is already enabled and globally
acknowledged at this point.

There's still a very small window between when the heap size reaches
the heap trigger and when the GC coordinator is able to stop the world
during which the mutator can allocate unabated. This allows *very*
rapidly allocator mutators like TestTraceStress to still occasionally
exceed the heap goal by a small amount (~20 MB at most for
TestTraceStress). However, this seems like a corner case.

Fixes #11677.

Change-Id: I0f80d949ec82341cd31ca1604a626efb7295a819
Reviewed-on: https://go-review.googlesource.com/12674Reviewed-by: Russ Cox <rsc@golang.org>

Currently we hand-code a set of phases when draining is allowed.
However, this set of phases is conservative. The critical invariant is
simply that the write barrier must be enabled if we're draining.

Shortly we're going to enable mutator assists during the scan phase,
which means we may drain during the scan phase. In preparation, this
commit generalizes these assertions to check the fundamental condition
that the write barrier is enabled, rather than checking that we're in
any particular phase.

Change-Id: I0e1bec1ca823d4a697a0831ec4c50f5dd3f2a893
Reviewed-on: https://go-review.googlesource.com/12673Reviewed-by: Russ Cox <rsc@golang.org>

Currently we clear both the mark 1 and mark 2 signals at the beginning
of concurrent mark. If either if these is clear, it acts as a signal
to the scheduler that it should start background workers. However,
this means that in the interim *between* mark 1 and mark 2, the
scheduler basically loops starting up new workers only to have them
return with nothing to do. In addition to harming performance and
delaying mutator work, this approach has a race where workers started
for mark 1 can mistakenly signal mark 2, causing it to complete
prematurely. This approach also interferes with starting assists
earlier to fix #11677.

Fix this by initially setting both mark 1 and mark 2 to "signaled".
The scheduler will not start background mark workers, though assists
can still run. When we're ready to enter mark 1, we clear the mark 1
signal and wait for it. Then, when we're ready to enter mark 2, we
clear the mark 2 signal and wait for it.

This structure also lets us deal cleanly with the situation where all
work is drained *prior* to the mark 2 wait, meaning that there may be
no workers to signal completion. Currently we deal with this using a
racy (and possibly incorrect) check for work in the coordinator itself
to skip the mark 2 wait if there's no work. This change makes the
coordinator unconditionally wait for mark completion and makes the
scheduler itself signal completion by slightly extending the logic it
already has to determine that there's no work and hence no use in
starting a new worker.

This is a prerequisite to fixing the remaining component of #11677,
which will require enabling assists during the scan phase. However, we
don't want to enable background workers until the mark phase because
they will compete with the scan. This change lets us use bgMark1 and
bgMark2 to indicate when it's okay to start background workers
independent of assists.

This is also a prerequisite to fixing #11694. It significantly reduces
the occurrence of long mark termination pauses in #11694 (from 64 out
of 1000 to 2 out of 1000 in one experiment).

Coincidentally, this also reduces the final heap size (and hence run
time) of TestTraceStress from ~100 MB and ~1.9 seconds to ~14 MB and
~0.4 seconds because it significantly shortens concurrent mark
duration.

Rick Hudson <rlh> did the hard work of tracking this down.

Change-Id: I12ea9ee2db9a0ae9d3a90dde4944a75fcf408f4c
Reviewed-on: https://go-review.googlesource.com/12672Reviewed-by: Russ Cox <rsc@golang.org>

Currently, there are three ways to satisfy a GC assist: 1) the mutator
steals credit from background GC, 2) the mutator actually does GC
work, and 3) there is no more work available. 3 was never really
intended as a way to satisfy an assist, and it causes problems: there
are periods when it's expected that the GC won't have any work, such
as when transitioning from mark 1 to mark 2 and from mark 2 to mark
termination. During these periods, there's no back-pressure on rapidly
allocating mutators, which lets them race ahead of the heap goal.

For example, test/init1.go and the runtime/trace test both have small
reachable heaps and contain loops that rapidly allocate large garbage
byte slices. This bug lets these tests exceed the heap goal by several
orders of magnitude.

Fix this by forcing the assist (and hence the allocation) to block
until it can satisfy its debt via either 1 or 2, or the GC cycle
terminates.

This fixes one the causes of #11677. It's still possible to overshoot
the GC heap goal, but with this change the overshoot is almost exactly
by the amount of allocation that happens during the concurrent scan
phase, between when the heap passes the GC trigger and when the GC
enables assists.

Change-Id: I5ef4edcb0d2e13a1e432e66e8245f2bd9f8995be
Reviewed-on: https://go-review.googlesource.com/12671Reviewed-by: Russ Cox <rsc@golang.org>

Currently it's possible for the GC assist to signal completion of the
mark phase, which puts the GC coordinator goroutine on the current P's
run queue, and then return to mutator code that delays until the next
forced preemption before actually yielding control to the GC
coordinator, dragging out completion of the mark phase. This delay can
be further exacerbated if the mutator makes other goroutines runnable
before yielding control, since this will push the GC coordinator on
the back of the P's run queue.

To fix this, this adds a Gosched to the assist if it completed the
mark phase. This immediately and directly yields control to the GC
coordinator. This already happens implicitly in the background mark
workers because they park immediately after completing the mark.

This is one of the reasons completion of the mark phase is being
dragged out and allowing the mutator to allocate without assisting,
leading to the large heap goal overshoot in issue #11677. This is also
a prerequisite to making the assist block when it can't pay off its
debt.

Change-Id: I586adfbecb3ca042a37966752c1dc757f5c7fc78
Reviewed-on: https://go-review.googlesource.com/12670Reviewed-by: Russ Cox <rsc@golang.org>

Currently it's possible to perform GC work on a system stack or when
locks are held if there's an allocation that triggers an assist. This
is generally a bad idea because of the fragility of these contexts,
and it's incompatible with two changes we're about to make: one is to
yield after signaling mark completion (which we can't do from a
non-preemptible context) and the other is to make assists block if
there's no other way for them to pay off the assist debt.

This commit simply skips the assist if it's called from a
non-preemptible context. The allocation will still count toward the
assist debt, so it will be paid off by a later assist. There should be
little allocation from non-preemptible contexts, so this shouldn't
harm the overall assist mechanism.

Change-Id: I7bf0e6c73e659fe6b52f27437abf39d76b245c79
Reviewed-on: https://go-review.googlesource.com/12649Reviewed-by: Russ Cox <rsc@golang.org>

When notetsleep_internal is called from notetsleepg, notetsleepg has
just given up the P, so write barriers are not allowed in
notetsleep_internal.

Change-Id: I1b214fa388b1ea05b8ce2dcfe1c0074c0a3c8870
Reviewed-on: https://go-review.googlesource.com/12647Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

Currently fractional and idle mark workers dispose of their gcWork
cache during mark 2 after incrementing work.nwait and after checking
whether there are any workers or any work available. This creates a
window for two races:

1) If the only remaining work is in this worker's gcWork cache, it
   will see that there are no more workers and no more work on the
   global lists (since it has not yet flushed its own cache) and
   prematurely signal mark 2 completion.

2) After this worker has incremented work.nwait but before it has
   flushed its cache, another worker may observe that there are no
   more workers and no more work and prematurely signal mark 2
   completion.

We can fix both of these by simply moving the cache flush above the
increment of nwait and the test of the completion condition.

This is probably contributing to #11694, though this alone is not
enough to fix it.

Change-Id: Idcf9656e5c460c5ea0d23c19c6c51e951f7716c3
Reviewed-on: https://go-review.googlesource.com/12646Reviewed-by: Russ Cox <rsc@golang.org>

GC assists are supposed to steal at most the amount of background GC
credit available so that background GC credit doesn't go negative.
However, they are instead stealing the *total* amount of their debt
but only claiming up to the amount of credit that was available. This
results in draining the background GC credit pool too quickly, which
results in unnecessary assist work.

The fix is trivial: steal the amount of work we meant to steal (which
is already computed).

Change-Id: I837fe60ed515ba91c6baf363248069734a7895ef
Reviewed-on: https://go-review.googlesource.com/12643Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

CL https://golang.org/cl/12470 has reportedly fixed the problems that
the misc/cgo/testsovar test encountered on darwin and netbsd.  Let's
actually run the test.

Update #10360.
Update #11654.

Change-Id: I4cdd27a8ec8713620e0135780a03f63cfcc538d0
Reviewed-on: https://go-review.googlesource.com/12702Reviewed-by: Russ Cox <rsc@golang.org>

This race was identified in #9796, but a sequence of fixes
proposed in golang.org/cl/4152 were rolled into
golang.org/cl/5910 which both fixed the race and
modified the name space behavior.

We rolled back the name space changes and lost the race fix.

Fix the race separate from the name space changes,
following the suggestion made by Roger Peppe in
https://go-review.googlesource.com/#/c/4152/7/src/encoding/xml/marshal.go@897

Fixes #9796.
Fixes #11885.

Change-Id: Ib2b68982da83dee9e04db8b8465a8295259bba46
Reviewed-on: https://go-review.googlesource.com/12687Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

Fixes build dashboard failures for android and nacl.

Change-Id: Id13896570061d3d8186f7b666ca1c37bcc789b0f
Reviewed-on: https://go-review.googlesource.com/12703Reviewed-by: David Crawshaw <crawshaw@golang.org>

Fixes #10348.

Change-Id: I3eea9738e3f6fdc1998d04a601dc9b556dd2db72
Reviewed-on: https://go-review.googlesource.com/12453Reviewed-by: Russ Cox <rsc@golang.org>

Currently the gctrace output reports the trigger heap size, rather
than the actual heap size at the beginning of GC. Often these are the
same, or at least very close. However, it's possible for the heap to
already have exceeded this trigger when we first check the trigger and
start GC; in this case, this output is very misleading. We've
encountered this confusion a few times when debugging and this
behavior is difficult to document succinctly.

Change the gctrace output to report the actual heap size when GC
starts, rather than the trigger.

Change-Id: I246b3ccae4c4c7ea44c012e70d24a46878d7601f
Reviewed-on: https://go-review.googlesource.com/12452Reviewed-by: Russ Cox <rsc@golang.org>

Whenever someone pastes gctrace output into GitHub, it helpfully turns
the GC cycle number into a link to some unrelated issue. Prevent this
by removing the pound before the cycle number. The fact that this is a
cycle number is probably more obvious at a glance than most of the
other numbers.

Change-Id: Ifa5fc7fe6c715eac50e639f25bc36c81a132ffea
Reviewed-on: https://go-review.googlesource.com/12413Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

Fixes #11839.

Change-Id: Ie092a3a512a2d35967364b41081a066ab3a6aab4
Reviewed-on: https://go-review.googlesource.com/12571Reviewed-by: Ian Lance Taylor <iant@golang.org>

svn dies due to not being able to validate the googlecode.com certificate.
hg does not even attempt to validate it.

Fixes #11806.

Change-Id: I84ced5aa84bb1e4a4cdb2254f2d08a64a1ef23f6
Reviewed-on: https://go-review.googlesource.com/12558Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes TestGoGetWorksWithVanityWildcards,
but that test uses the network and is not run
on the builders.

For #11806.

Change-Id: I35c6677deaf84e2fa9bdb98b62d80d388b5248ae
Reviewed-on: https://go-review.googlesource.com/12557Reviewed-by: Ian Lance Taylor <iant@golang.org>

This extends https://golang.org/cl/2811, which only applied to Darwin
and GNU/Linux, to all Unix systems.

Fixes #9591.

Change-Id: Iec3fb438564ba2924b15b447c0480f87c0bfd009
Reviewed-on: https://go-review.googlesource.com/12661
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

Broke most builders.

This reverts commit a60c5366.

Change-Id: Iae952cfcc73ef5da621616a0b3d586b60d1ce9c9
Reviewed-on: https://go-review.googlesource.com/12684Reviewed-by: Russ Cox <rsc@golang.org>

Change-Id: Ib4fb8256863d908580a07e6f2e1c92ea109ea989
Reviewed-on: https://go-review.googlesource.com/11249Reviewed-by: Russ Cox <rsc@golang.org>

Fixes #11343.

Change-Id: I46efc24b687b9d060ad864fbb238c74544348e38
Reviewed-on: https://go-review.googlesource.com/12556Reviewed-by: Rob Pike <r@golang.org>

Fixes #11020

Change-Id: I52760a01420a11f3c979f678812b3775a3af61e4
Reviewed-on: https://go-review.googlesource.com/12545Reviewed-by: Russ Cox <rsc@golang.org>

From https://github.com/golang/go/issues/11745#issuecomment-123555313 :

The http.RoundTripper interface says you get either a *Response, or an
error.

But in the case of a client writing a large request and the server
replying prematurely (e.g. 403 Forbidden) and closing the connection
without reading the request body, what does the client want? The 403
response, or the error that the body couldn't be copied?

This CL implements the aforementioned comment's option c), making the
Transport give an N millisecond advantage to responses over body write
errors.

Updates #11745

Change-Id: I4485a782505d54de6189f6856a7a1f33ce4d5e5e
Reviewed-on: https://go-review.googlesource.com/12590Reviewed-by: Russ Cox <rsc@golang.org>

Change-Id: I9b8a6ac1ff6bef3b7f1e033bfd029f2a59e30297
Reviewed-on: https://go-review.googlesource.com/12623Reviewed-by: Russ Cox <rsc@golang.org>

Fixes #11872.

Change-Id: Ibc7d8438374c9d90fd4cbefb61426c7f4f96af0d
Reviewed-on: https://go-review.googlesource.com/12691Reviewed-by: Russ Cox <rsc@golang.org>

We used to use build.Import to get the dependencies, but that meant
we had to repeat the check for every possible GOOS/GOARCH/cgo
combination, which took too long. So we made the test in short mode
only check the current GOOS/GOARCH/cgo combination.
But some combinations can't run the test at all. For example darwin/arm64
does not run tests with a full source file systems, so it cannot test itself,
so nothing was testing darwin/arm64. This led to bugs like #10455
not being caught.

Rewrite the test to read the imports out of the source files ourselves,
so that we can look at all source files in a directory in one pass,
regardless of which GOOS/GOARCH/cgo/etc they require.
This one complete pass runs in the same amount of time as the
old single combination check ran, so we can now test all systems,
even in short mode.

Change-Id: Ie216303c2515bbf1b6fb717d530a0636e271cb6d
Reviewed-on: https://go-review.googlesource.com/12576Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change adds new methods to Decoder.

 * Decoder.Token steps through a JSON document, returning a value for each token.
 * Decoder.Decode unmarshals the entire value at the token stream's current
   position (in addition to its existing function in a stream of JSON values)

Fixes #6050.
Fixes #6499.

Change-Id: Iff283e0e7b537221ae256392aca6529f06ebe211
Reviewed-on: https://go-review.googlesource.com/9073Reviewed-by: Russ Cox <rsc@golang.org>

A while back we discovered that the dependencies test allowed
arbitrary dependencies for packages we forgot to list.
To stop the damage we added a grandfathered list and fixed
the code to expect unlisted packages to have no dependencies.

This CL replaces the grandfathered list with some more
careful placement of dependency rules.

Thankfully, there were no terrible inversions.

Fixes #10487.

Change-Id: I5a6f92435bd2c66c47ec8ab629edbd88b189f028
Reviewed-on: https://go-review.googlesource.com/12575Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

It's not clear this really belongs anywhere at all,
but this is a better place for it than package os.
This way package os can avoid importing "C".

Fixes #10455.

Change-Id: Ibe321a93bf26f478951c3a067d75e22f3d967eb7
Reviewed-on: https://go-review.googlesource.com/12574Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

It was not running because of invalid use of ArchChar.
I didn't catch this when I scrubbed ArchChar from the tree
because this code wasn't in the tree yet.

The test seems to pass, which is nice.

Change-Id: I59761a7a04a73681e147e25c1e7f010068276aa8
Reviewed-on: https://go-review.googlesource.com/12573Reviewed-by: Robert Griesemer <gri@golang.org>

There is clearly work to do here with respect to xml name spaces,
but I don't believe the changes in this cycle are clearly correct.
The changes in this cycle have visible impact on the generated xml,
possibly breaking existing programs, and yet it's not clear that they
are the end of the story: there is still significant confusion about how
name spaces work or should work (see #9519, #9775, #8167, #7113).

I would like to wait to make breaking changes until we completely
understand what the behavior should be and can evaluate the benefit
of those breaking changes. My main concern here is that we will break
programs in Go 1.5 for the sake of name space adjustments and then
while trying to fix those other bugs we'll break programs in Go 1.6 too.
Let's wait until we know all the changes we want to make before we
decide whether or how to break existing programs.

This CL reverts:

5ae822ba encoding/xml: minor changes
bb7e6656 encoding/xml: fix xmlns= behavior
9f9d66d3 encoding/xml: fix default namespace of tags
b69ea018 encoding/xml: fix namespaces in a>b tags
3be158d6 encoding/xml: encoding name spaces correctly

and adjusts tests from

a9dddb53 encoding/xml: add more EncodeToken tests.

to expect Go 1.4 behavior.

I have confirmed that the name space parts of the test suite
as of this CL passes against the Go 1.4 encoding/xml package,
indicating that this CL successfully restores the Go 1.4 behavior.

(Other tests do not, but that's because there were some real
bug fixes in this cycle that are being kept. Specifically, the
tests that don't pass in Go 1.4 are TestMarshal's NestedAndComment
case, TestEncodeToken's encoding of newlines, and
TestSimpleUseOfEncodeToken returning an error for invalid
token types.)

I also checked that the Go 1.4 tests pass when run against
this copy of the sources.

Fixes #11841.

Change-Id: I97de06761038b40388ef6e3a55547ff43edee7cb
Reviewed-on: https://go-review.googlesource.com/12570Reviewed-by: Nigel Tao <nigeltao@golang.org>

The "add a Request.Cancel channel" change (https://golang.org/cl/11601)
added support for "race free" cancellation, but introduced a data race. :)

Noticed while running "go test -race net/http". The test is skipped in
short mode, so we never saw it on the dashboard.

Change-Id: Ica14579d8723f8f9d1691e8d56c30b585b332c64
Reviewed-on: https://go-review.googlesource.com/12663Reviewed-by: Aaron Jacobs <jacobsa@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I2c21b012534be20443157c6b77ef21bd585902b0
Reviewed-on: https://go-review.googlesource.com/12636Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Not everyone is aware that go build is a wrapper for other
tools. Mention this in the text for go help build so people using
other build systems won't just wrap go build, which is usually a
mistake (it doesn't do incremental builds by default, for instance).

Update #11854.

Change-Id: I759f91f23ccd3671204c39feea12a3bfaf9f0114
Reviewed-on: https://go-review.googlesource.com/12625Reviewed-by: Ian Lance Taylor <iant@golang.org>

The system stack is only around 8kb on ARM so one can't put an 8kb buffer on
the stack. More than 1024 ARM cores seems sufficiently unlikely for the
foreseeable future.

Fixes #11853

Change-Id: I7cb27c1250a6153f86e269c172054e9dfc218c72
Reviewed-on: https://go-review.googlesource.com/12622Reviewed-by: Austin Clements <austin@google.com>

Fixes #9530.

Change-Id: Iadfc027c7164e3ba35adb5c67deb42b51d3498ca
Reviewed-on: https://go-review.googlesource.com/12603Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dave Cheney <dave@cheney.net>

Currently TestDoDupSuppress can fail if the goroutines created by its
loop run sequentially. This is rare, but it has caused failures on the
dashboard and in stress testing.

While I think there's no way to eliminate all possible thread
schedules that could make this test fail because it depends on waiting
until a Group.Do blocks, it is possible to make it much more robust.

This commit deflakes this test by forcing at least one invocation of
fn to start and all goroutines to reach the line just before the Do
call before allowing fn to proceed. fn then waits 10 milliseconds
before returning to allow the goroutines to pass through the Do.

With this change, in 50,000 runs of the stress testing configuration,
the number of calls to fn never even exceeded 1.

Fixes #11784.

Change-Id: Ie5adf5764545050ec407619769a656251c4cff04
Reviewed-on: https://go-review.googlesource.com/12681Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Update the docs to explain the code added in
commit 67e1d400.

Fixes #11831.

Change-Id: I8fe72e449507847c4bd9d77de40947ded7f2ff9d
Reviewed-on: https://go-review.googlesource.com/12515Reviewed-by: Dave Cheney <dave@cheney.net>

Change-Id: I102901e3df76830ccd5ab74d757203d103eef9e8
Reviewed-on: https://go-review.googlesource.com/12657Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>