In a typical HTTP request, the client writes the request, and
then the server replies. Go's HTTP client code (Transport) has
two goroutines per connection: one writing, and one reading. A
third goroutine (the one initiating the HTTP request)
coordinates with those two.

Because most HTTP requests are done when the server replies,
the Go code has always handled connection reuse purely in the
readLoop goroutine.

But if a client is writing a large request and the server
replies before it's consumed the entire request (e.g. it
replied with a 403 Forbidden and had no use for the body), it
was possible for Go to re-select that connection for a
subsequent request before we were done writing the first. That
wasn't actually a data race; the second HTTP request would
just get enqueued to write its request on the writeLoop. But
because the previous writeLoop didn't finish writing (and
might not ever), that connection is in a weird state. We
really just don't want to get into a state where we're
re-using a connection when the server spoke out of turn.

This CL changes the readLoop goroutine to verify that the
writeLoop finished before returning the connection.

In the process, it also fixes a potential goroutine leak where
a connection could close but the recycling logic could be
blocked forever waiting for the client to read to EOF or
error. Now it also selects on the persistConn's close channel,
and the closer of that is no longer the readLoop (which was
dead locking in some cases before). It's now closed at the
same place the underlying net.Conn is closed. This likely fixes
or helps Issue 7620.

Also addressed some small cosmetic things in the process.

Update #7620
Fixes #7569

LGTM=adg
R=golang-codereviews, adg
CC=dsymonds, golang-codereviews, rsc
https://golang.org/cl/86290043

We originally decided to skip this test in short mode
to prevent the parallel runtime test to timeout on the
Plan 9 builder. This should no longer be required since
the issue was fixed in CL 86210043.

LGTM=dave, bradfitz
R=dvyukov, dave, bradfitz
CC=golang-codereviews, rsc
https://golang.org/cl/84790044

If you pass ns = 100,000 to this function, timediv will
return ms = 0. tsemacquire in /sys/src/9/port/sysproc.c
will return immediately when ms == 0 and the semaphore
cannot be acquired immediately - it doesn't sleep - so
notetsleep will spin, chewing cpu and repeatedly reading
the time, until the 100us have passed.

Thanks to the time reads it won't take too many iterations,
but whatever we are waiting for does not get a chance to
run. Eventually the notetsleep spin loop returns and we
end up in the stoptheworld spin loop - actually a sleep
loop but we're not doing a good job of sleeping.

After 100ms or so of this, the kernel says enough and
schedules a different thread. That thread manages to do
whatever we're waiting for, and the spinning in the other
thread stops. If tsemacquire had actually slept, this
would have happened much quicker.

Many thanks to Russ Cox for help debugging.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/86210043

All that's left is net/http and the stuff I need help describing: FreeBSD and Windows.

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/86320043

even when there are no *_test.go files present.
rsc suggested this change

Fixes #7108

LGTM=r, adg
R=golang-codereviews, r, adg
CC=golang-codereviews
https://golang.org/cl/84300043

The buffer length should be the size in bytes
instead of the number of structs.

Fixes #6588.

LGTM=mikioh.mikioh
R=golang-codereviews, mikioh.mikioh, adg
CC=golang-codereviews
https://golang.org/cl/84830043

Generated by addca.

R=gobot
CC=golang-codereviews
https://golang.org/cl/85550044

bufio: undo incorrect bug fix

««« original CL description
bufio: fix potential endless loop in ReadByte

Fixes #7745.

LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/86220044
»»»

LGTM=adg
R=r, adg
CC=golang-codereviews
https://golang.org/cl/85550045

Fixes #7745.

LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/86220044

Also:
- fix error messages in tests
- make tests more symmetric

Fixes #7607.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/86180043

Explain what its purpose is and give examples of good and bad use.
Fixes #7167.

LGTM=dvyukov, rsc
R=golang-codereviews, dvyukov, rsc
CC=golang-codereviews
https://golang.org/cl/85880044

On amd64p32 pointers are 32-bit-aligned and cannot be assumed to
have an offset multiple of widthreg. Instead check that they are
withptr-aligned.

Also change the threshold for region merging to 2*widthreg
instead of 2*widthptr because performance on amd64 and amd64p32
is expected to be the same.

Fixes #7712.

LGTM=khr
R=rsc, dave, khr, brad, bradfitz
CC=golang-codereviews
https://golang.org/cl/84690044

go-mode on Emacs 23 wrongly recognizes a backquote in a comment or
a string as a start of a raw string literal. Below is an example
that go-mode does not work well. This patch is to fix that issue.

  // `
  var x = 1
  // `

LGTM=dominik.honnef
R=golang-codereviews, dominik.honnef, adonovan
CC=golang-codereviews
https://golang.org/cl/84900043

Cuts the number of calls from 6 to 2 in the non-debug case.

LGTM=iant
R=golang-codereviews, iant
CC=0intro, aram, golang-codereviews, khr
https://golang.org/cl/86040043

Suggested in comments on CL 85740043.

LGTM=aram
R=golang-codereviews, aram
CC=dave, golang-codereviews, r
https://golang.org/cl/85990044

TBR=iant
CC=golang-codereviews
https://golang.org/cl/86030043

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/85890043

Fixes #6889

LGTM=rsc
R=gri, rsc
CC=golang-codereviews
https://golang.org/cl/85080044

Fixes #7538

LGTM=rsc
R=gri, rsc
CC=golang-codereviews
https://golang.org/cl/85040045

1) The code to catch an exception marked the template as escaped
when it was not yet, which caused subsequent executions of the
template to not escape properly.
2) ensurePipelineContains needs to handled Field as well as
Identifier nodes.

Fixes #7379.

LGTM=mikesamuel
R=mikesamuel
CC=golang-codereviews
https://golang.org/cl/85240043

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/85840043

Getenv() should not call malloc when called from
gotraceback(). Instead, we return a static buffer
in this case, with enough room to hold the longest
value.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/85680043

LGTM=rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/85740043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/85760043

On Plan 9 gotraceback calls getenv calls malloc, and we gotraceback
on every call to gentraceback, which happens during garbage collection.
Honestly I don't even know how this works on Plan 9.
I suspect it does not, and that we are getting by because
no one has tried to run with $GOTRACEBACK set at all.

This will speed up all the other systems by epsilon, since they
won't call getenv and atoi repeatedly.

LGTM=bradfitz
R=golang-codereviews, bradfitz, 0intro
CC=golang-codereviews
https://golang.org/cl/85430046

Add a $Context variable to the template so that the build.Context values
such as BuildTags can be accessed.

Fixes #6666.

LGTM=adg, rsc
R=golang-codereviews, gobot, adg, rsc
CC=golang-codereviews
https://golang.org/cl/72770043

Short circuit for calling values funcs by MakeFunc was placed
before variadic arg rearrangement code in reflect.call.
Fixes #7534.

LGTM=khr
R=golang-codereviews, bradfitz, khr, rsc
CC=golang-codereviews
https://golang.org/cl/75370043

Generated by addca.

R=gobot
CC=golang-codereviews
https://golang.org/cl/85820043

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/85720043

Now that we have a constant-time P-256 implementation, it's worth
paying more attention elsewhere.

The inversion of k in (EC)DSA was using Euclid's algorithm which isn't
constant-time. This change switches to Fermat's algorithm, which is
much better. However, it's important to note that math/big itself isn't
constant time and is using a 4-bit window for exponentiation with
variable memory access patterns.

(Since math/big depends quite deeply on its values being in minimal (as
opposed to fixed-length) represetation, perhaps crypto/elliptic should
grow a constant-time implementation of exponentiation in the scalar
field.)

R=bradfitz
Fixes #7652.

LGTM=rsc
R=golang-codereviews, bradfitz, rsc
CC=golang-codereviews
https://golang.org/cl/82740043

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/85660043

LGTM=dvyukov, iant, rsc
R=golang-codereviews, dvyukov, iant, rsc
CC=golang-codereviews
https://golang.org/cl/85250043

Permit paired parentheses in URLs such as:

http://en.wikipedia.org/wiki/Camellia_(cipher)

Fixes #5043.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/85610043

Fixes #6836.

LGTM=rsc
R=golang-codereviews, rsc, r, mike
CC=golang-codereviews
https://golang.org/cl/33140043

Fixes #7614.

LGTM=rsc
R=golang-codereviews, r, rsc, dan.kortschak, applezinc
CC=golang-codereviews
https://golang.org/cl/79210044

Generated by addca.

R=gobot
CC=golang-codereviews
https://golang.org/cl/85490043

Given
        type Outer struct {
                *Inner
                ...
        }
the compiler generates the implementation of (*Outer).M dispatching to
the embedded Inner. The implementation is logically:
        func (p *Outer) M() {
                (p.Inner).M()
        }
but since the only change here is the replacement of one pointer
receiver with another, the actual generated code overwrites the
original receiver with the p.Inner pointer and then jumps to the M
method expecting the *Inner receiver.

During reflect.Value.Call, we create an argument frame and the
associated data structures to describe it to the garbage collector,
populate the frame, call reflect.call to run a function call using
that frame, and then copy the results back out of the frame. The
reflect.call function does a memmove of the frame structure onto the
stack (to set up the inputs), runs the call, and the memmoves the
stack back to the frame structure (to preserve the outputs).

Originally reflect.call did not distinguish inputs from outputs: both
memmoves were for the full stack frame. However, in the case where the
called function was one of these wrappers, the rewritten receiver is
almost certainly a different type than the original receiver. This is
not a problem on the stack, where we use the program counter to
determine the type information and understand that during (*Outer).M
the receiver is an *Outer while during (*Inner).M the receiver in the
same memory word is now an *Inner. But in the statically typed
argument frame created by reflect, the receiver is always an *Outer.
Copying the modified receiver pointer off the stack into the frame
will store an *Inner there, and then if a garbage collection happens
to scan that argument frame before it is discarded, it will scan the
*Inner memory as if it were an *Outer. If the two have different
memory layouts, the collection will intepret the memory incorrectly.

Fix by only copying back the results.

Fixes #7725.

LGTM=khr
R=khr
CC=dave, golang-codereviews
https://golang.org/cl/85180043

It turns out there is a relatively common pattern that relies on
inverted channel semaphore:

gate := make(chan bool, N)
for ... {
        // limit concurrency
        gate <- true
        go func() {
                foo(...)
                <-gate
        }()
}
// join all goroutines
for i := 0; i < N; i++ {
        gate <- true
}

So handle synchronization on inverted semaphores with cap>1.
Fixes #7718.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/84880046

This code tests linkmode == LinkExternal but is only invoked
by the compiler/assembler, not the linker.

Update #7164

LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/85080043

LGTM=bradfitz, alex.brainman
R=golang-codereviews, bradfitz, alex.brainman
CC=golang-codereviews
https://golang.org/cl/85190043