Rename the interface that specifies methods to be implemented by trace
receivers. Reason is that in the next patch we'll need to expose
"Tracer" as the tracing networker itself.

Generate g for ~ Go 1.16beta1 (go1.16beta1-34-g4fd9455882)
Compared to Go1.15 there are only cosmetic changes:

    --- a/zruntime_g_go1.15.go
    +++ b/zruntime_g_go1.16.go
    @@ -1,6 +1,6 @@
     // Code generated by g_typedef; DO NOT EDIT.

    -// +build go1.15,!go1.16
    +// +build go1.16,!go1.17

     package xruntime

    @@ -144,7 +144,7 @@ type gobuf struct {
     	ctxt unsafe.Pointer
     	ret  uintreg
     	lr   uintptr
    -	bp   uintptr // for GOEXPERIMENT=framepointer
    +	bp   uintptr // for framepointer-enabled architectures
     }
     type funcval struct {
     	fn uintptr
    @@ -158,6 +158,8 @@ type timer struct {
     	// Timer wakes up at when, and then at when+period, ... (period > 0 only)
     	// each time calling f(arg, now) in the timer goroutine, so f must be
     	// a well-behaved function and not block.
    +	//
    +	// when must be positive on an active timer.
     	when   int64
     	period int64
     	f      func(interface{}, uintptr)

Regenerated files stay without changes for Go1.15 and previous releases.

When a virtnet network - e.g. lonet - is explicitly used in tests, the
open and close sequence is easy to implement:

    network = lonet.Join(...)
    defer network.Close()

    hostα = network.NewHost("α")
    defer hostα.Close()
    hostβ = network.NewHost("β")
    defer hostβ.Close()
    ...

However in other scenarios - for example when the code wants to call
xnet.Networker factory that creates a networker out of several potential
choices according to given parameters, only interface for network
access-point (e.g. Host in lonet/virtnet case) is returned. The network
itself (virtnet.SubNetwork) is not returned to the user. As it is this
makes it impossible to close the network and release its resources.

Instead of adding complexity to such "create-networker" functions to
e.g. change Close of returned networker to also close subnetwork, or
return both networker and a separate close func, let's teach virtnet to
close SubNetwork automatically when last host of this subnetwork is
closed. Make it opt-in since this behaviour is not universally wanted.

This way a factory that is asked to connect to network as e.g. a node on
lonet, could do the following:

    func neonet.Join(...) xnet.Networker {
        ...
        // join lonet "<net>" as host "<node>"
        network = lonet.Join("<net>")
        host = network.NewHost("<node>")
        network.AutoClose() // host.Close will close network
        return host
    }

and network will be closed on host.Close() call.

-> Add SubNetwork.AutoClose to schedule Close to be called after last host on the subnetwork is closed.
-> Mirror this change in virtnet part of lonet.py

Even though there is no need to manually release resources for NetPlain
and NetTLS, for other networkers - for example lonet - releasing
resources is needed. In general programs cannot always use lonet
explicitly, as there might be a factory function that creates a
Networker according to given parameters.

-> Adjust Networker interface to include general Close.
-> Adjust NetPlain to follow added "interrupt-on-close" semantic for uniformity.

Similarly to what we do in package xio (see 7ad867a3 "xio: Add
Reader/Writer/... interfaces - io analogs that add support for
contexts"), add utilities to bind xnet.Listener to context (giving
net.Listener), and, on the other hand, adapt uncontextified net.Listener
to xnet.Listener that handles cancellation.

This utilities are needed because a lot of third-party code wants to
work with net.Listener interface only.

Contrary to xio, we can make it working reliably in both ways (because
Accept already buffers accepting connections starting at OS level).

In the previous patch xnet.Networker was changed: Listen now accepts ctx
and returns xnet.Listener instead of net.Listener.

-> Adapt the code all around to that.

We already handle cancellation in Dial, but Accepting was out of luck
until now. This makes it more difficult for clients to implement and
wrap acceptors where they need to handle cancellations. This also makes
it possible for a test or program to get stuck in Accept loop if it is
not careful enough to manually handle ctx cancel around Accept calls.

-> Fix it in one place - here, in xnet - so that users are offloaded
from all this and can just call Accept(ctx) and rely on underlying
implementation to handle ctx cancel.

This patch:

- introduces xnet.Listener interface, which is like net.Listener, but
  Accept goes with ctx argument.
- changes Networker.Listen signature to return xnet.Listener instead of
  net.Listener. While we are here - changing it - also add ctx argument
  to Listen call itself.
- Adds listenerCtx - which, given net.Listener, provides xnet.Listener
  by wrapping some logic around original.
- Adapts NetPlain, NetTLS and NetTrace to provide updated interface.

We'll fix up everything in other packages to match/use updated interface
in the next patch.

See nexedi/pygolang@21756bd3.

Go1.14.10 and Go1.15.3 changed internal structure of g:

https://github.com/golang/go/commit/878da0bf881b (go1.14)
https://github.com/golang/go/commit/bf79f91d3dc4 (go1.15)

A shorthand for when exception context is just formatted string.
Simplifies

	func doSomething(path string) {
		defer exc.Context(func() interface{} {
			return fmt.Sprintf("doing something %s", path)
		})()
		...

to

	func doSomething(path string) {
		defer exc.Contextf("doing something %s", path)
		...

`go mod init` + build/test that fetched in dependencies.

It was address-of error (the type) instead of &err.

https://github.com/golang/go/issues/36503
https://github.com/golang/go/issues/36448

They are there for 6 months already without being considered for real
and so the progress is very unlikely, but still...

Generate g for ~ Go 1.15beta1 (go1.14beta1-1729-gc0e8e405c0)
Compared to Go1.14 there are no changes.

Regenerated files stay without changes for Go1.14 and previous releases.

Provide race.Enabled for programs to know whether they were built with
race detector or not.

Code originates from https://lab.nexedi.com/kirr/wendelin.core/tree/25c3184d/wcfs/internal/race
See also: https://github.com/golang/go/issues/36477.

So that Go1.13 and golang.org/x/xerrors understand the wrapping:
https://blog.golang.org/go1.13-errors

Preserve Cause for compatibility with github.com/pkg/errors.

Add xsync.WorkGroup that is similar to https://godoc.org/golang.org/x/sync/errgroup,
but amends it with a bit better (imho) design where work context is
explicitly passed into worker (see also [1]). This mirrors sync.WorkGroup that we
already have at Pygolang side [2].

[1] https://github.com/golang/go/issues/34510
[2] https://pypi.org/project/pygolang/#concurrency

I need this to support sysread(/head/watch) cancellation in WCFS
filesystem [1,2,3].

[1] wendelin.core@b17aeb8c
[2] wendelin.core@f05271b1
[3] wendelin.core@5ba816da

Rework Pipe to create (xio.Reader, xio.Writer) instead of (io.Reader,
io.Writer) and teach xio.Pipe{Reader,Writer} to accept ctx argument and
handle cancellation.

I need this to support sysread(/head/watch) cancellation in WCFS
filesystem [1,2,3]. See also [4].

[1] wendelin.core@b17aeb8c
[2] wendelin.core@f05271b1
[3] wendelin.core@5ba816da
[4] https://github.com/golang/go/issues/20280

Just make it compile by trivially adapting the code to refer thing from
io package. Change license reference to the place where Go license lives
in go123 (LICENSE-go, added in ad78da1b "xflag: Add counting flag from
go.git internals").

This is pristine copy of pipe.go + tests from Go go1.14beta1-24-g075c20cea8 .
We'll adapt copied code to xio and add cancellation support in further commits.

Done toprovide uniform API in xio package.
Compensate for API change in places where xio.CountReader was used.

In many cases IO needs to be able to be canceled. For example in WCFS
filesystem I need to cancel handling sysread(/head/watch) when FUSE
INTERRUPT request comes in [1,2,3]. The READ handler for /head/watch
inside WCFS is interally implemented via io.Pipe which does not provide
read/write cancellattion besides "destructive" close.

Standard Go answer for cancellations is via contexts. So as a first step
let's add corresponding interfaces - xio.Reader, xio.Writer etc - that
are io analogs that add support for contexts.

For compatibility with legacy code that work with only io.X (e.g.  only
with io.Reader), in spirit of [4], add BindCtx which binds xio.X
instance with context and converts it into io.X. Add WithCtx -
corresponding inverse operation that converts io.X back into xio.X and
for general io.X adds cancellation handling on a best-effort basis.

[1] wendelin.core@b17aeb8c
[2] wendelin.core@f05271b1
[3] wendelin.core@5ba816da
[4] https://github.com/golang/go/issues/20280
[5] https://github.com/golang/go/issues/16522

Generate g for ~ Go 1.14beta1 (go1.14beta1-10-g5c6f42773c)
Compared to Go1.13 there are several changed to g, _defer and timer
related to:

- non-cooperative preemption (https://golang.org/issue/10958, https://golang.org/issue/24543);
- inlined defers (https://golang.org/issue/14939, https://golang.org/issue/34481);
- timers rework to be integrated with network poller (https://golang.org/issue/6239, https://golang.org/issue/27707):

Regenerated files stay without changes for Go1.13 and previous releases.

---- 8< ----
diff --git a/zruntime_g_go1.13.go b/zruntime_g_go1.14.go
index 76851fd..19cebae 100644
--- a/zruntime_g_go1.13.go
+++ b/zruntime_g_go1.14.go
@@ -1,6 +1,6 @@
 // Code generated by g_typedef; DO NOT EDIT.

-// +build go1.13,!go1.14
+// +build go1.14,!go1.15

 package xruntime

@@ -32,12 +32,25 @@ type g struct {
 	schedlink    guintptr
 	waitsince    int64      // approx time when the g become blocked
 	waitreason   waitReason // if status==Gwaiting
+
 	preempt       bool // preemption signal, duplicates stackguard0 = stackpreempt
+	preemptStop   bool // transition to _Gpreempted on preemption; otherwise, just deschedule
+	preemptShrink bool // shrink stack at synchronous safe point
+
+	// asyncSafePoint is set if g is stopped at an asynchronous
+	// safe point. This means there are frames on the stack
+	// without precise pointer information.
+	asyncSafePoint bool
+
 	paniconfault bool // panic (instead of crash) on unexpected fault address
-	preemptscan    bool       // preempted g does scan for gc
 	gcscandone   bool // g has scanned stack; protected by _Gscan bit in status
-	gcscanvalid    bool       // false at start of gc cycle, true if G has not run since last scan; TODO: remove?
 	throwsplit   bool // must not split stack
+	// activeStackChans indicates that there are unlocked channels
+	// pointing into this goroutine's stack. If true, stack
+	// copying needs to acquire channel locks to protect these
+	// areas of the stack.
+	activeStackChans bool
+
 	raceignore     int8     // ignore race detection events
 	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
 	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
@@ -76,18 +89,37 @@ type _panic struct {
 	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
 	arg       interface{}    // argument to panic
 	link      *_panic        // link to earlier panic
+	pc        uintptr        // where to return to in runtime if this panic is bypassed
+	sp        unsafe.Pointer // where to return to in runtime if this panic is bypassed
 	recovered bool           // whether this panic is over
 	aborted   bool           // the panic was aborted
+	goexit    bool
 }
 type _defer struct {
 	siz     int32 // includes both arguments and results
 	started bool
 	heap    bool
+	// openDefer indicates that this _defer is for a frame with open-coded
+	// defers. We have only one defer record for the entire frame (which may
+	// currently have 0, 1, or more defers active).
+	openDefer bool
 	sp        uintptr  // sp at time of defer
-	pc      uintptr
-	fn      *funcval
+	pc        uintptr  // pc at time of defer
+	fn        *funcval // can be nil for open-coded defers
 	_panic    *_panic  // panic that is running defer
 	link      *_defer
+
+	// If openDefer is true, the fields below record values about the stack
+	// frame and associated function that has the open-coded defer(s). sp
+	// above will be the sp for the frame, and pc will be address of the
+	// deferreturn call in the function.
+	fd   unsafe.Pointer // funcdata for the function associated with the frame
+	varp uintptr        // value of varp for the stack frame
+	// framepc is the current pc associated with the stack frame. Together,
+	// with sp above (which is the sp associated with the stack frame),
+	// framepc/sp can be used as pc/sp pair to continue a stack trace via
+	// gentraceback().
+	framepc uintptr
 }
 type gobuf struct {
 	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
@@ -114,8 +146,10 @@ type funcval struct {
 	fn uintptr
 }
 type timer struct {
-	tb *timersBucket // the bucket the timer lives in
-	i  int           // heap index
+	// If this timer is on a heap, which P's heap it is on.
+	// puintptr rather than *p to match uintptr in the versions
+	// of this struct defined in other packages.
+	pp puintptr

 	// Timer wakes up at when, and then at when+period, ... (period > 0 only)
 	// each time calling f(arg, now) in the timer goroutine, so f must be
@@ -125,6 +159,12 @@ type timer struct {
 	f      func(interface{}, uintptr)
 	arg    interface{}
 	seq    uintptr
+
+	// What to set the when field to in timerModifiedXX status.
+	nextwhen int64
+
+	// The status field holds one of the values below.
+	status uint32
 }
 type guintptr uintptr
 type puintptr uintptr

Generate g for ~ Go 1.13beta2 (go1.13beta1-91-ga25c2878c7).
Compared to Go1.12 _defer gains `heap bool` member. No other shanges.

Pygolang does it. However my comment on Go issue tracker about this
topic got no feedback at all:

https://github.com/golang/go/issues/30694#issuecomment-483820400

As of Go1.12 the check for whether particular trace event is enabled or
not is inlined into caller. For example:

	---- 8< ---- (connection.go)
	//trace:event traceMsgSendPre(l *NodeLink, connId uint32, msg proto.Msg)

	func (link *NodeLink) sendMsg(connId uint32, msg proto.Msg) error {
		traceMsgSendPre(link, connId, msg)

		buf := msgPack(connId, msg)
		return link.sendPkt(buf)
	}

	---- 8< ---- (ztrace.go)
	// traceevent: traceMsgSendPre(l *NodeLink, connId uint32, msg proto.Msg)

	type _t_traceMsgSendPre struct {
	        tracing.Probe
	        probefunc     func(l *NodeLink, connId uint32, msg proto.Msg)
	}

	var _traceMsgSendPre *_t_traceMsgSendPre

	func traceMsgSendPre(l *NodeLink, connId uint32, msg proto.Msg) {
	        if _traceMsgSendPre != nil {
	                _traceMsgSendPre_run(l, connId, msg)
	        }
	}

	func _traceMsgSendPre_run(l *NodeLink, connId uint32, msg proto.Msg) {
	        for p := _traceMsgSendPre; p != nil; p = (*_t_traceMsgSendPre)(unsafe.Pointer(p.Next())) {
	                p.probefunc(l, connId, msg)
	        }
	}

	---- 8< ---- (connection.o)
	TEXT lab·nexedi·com∕kirr∕neo∕go∕neo∕neonet·(*NodeLink).sendMsg(SB), ABIInternal, $40-48 // connection.go:1368
	        // MOVQ    (TLS), CX (stack growth prologue)
	        // CMPQ    SP, 16(CX)
	        // JLS     177
	        // SUBQ    $40, SP
	        // MOVQ    BP, 32(SP) (BP save)
	        // LEAQ    32(SP), BP (BP init)
	        // FUNCDATA $0, gclocals·dbae954985b577993f0eafab1347dd21(SB) (args)
	        FUNCDATA   $1, gclocals·f6bd6b3389b872033d462029172c8612(SB) (locals)
	        FUNCDATA   $3, gclocals·47f0f3578d0f16ef296c57af2564832c(SB)
	        PCDATA     $2, $0             // connection.go:1369
	        PCDATA     $0, $0
	        XCHGL      AX, AX
	        CMPQ       lab·nexedi·com∕kirr∕neo∕go∕neo∕neonet·_traceMsgSendPre(SB), $0	<-- inlined traceMsgSendPre
	        JNE        pc130              // ztrace.go:50					<--
	pc44:
	        MOVL       connId+56(SP), AX  // connection.go:1371				<-- normal path
	        MOVL       AX, (SP)
	        MOVQ       msg+64(SP), AX
	        MOVQ       AX, 8(SP)
	        PCDATA     $2, $1
	        PCDATA     $0, $1
	        MOVQ       msg+72(SP), AX
	        PCDATA     $2, $0
	        MOVQ       AX, 16(SP)
	        CALL       lab·nexedi·com∕kirr∕neo∕go∕neo∕neonet·msgPack(SB)
	        PCDATA     $2, $1
	        MOVQ       24(SP), AX
	        PCDATA     $2, $2             // connection.go:1372
	        PCDATA     $0, $2
	        MOVQ       link+48(SP), CX
	        PCDATA     $2, $1
	        MOVQ       CX, (SP)
	        PCDATA     $2, $0
	        MOVQ       AX, 8(SP)
	        CALL       lab·nexedi·com∕kirr∕neo∕go∕neo∕neonet·(*NodeLink).sendPkt(SB)
	        PCDATA     $2, $1
	        MOVQ       24(SP), AX
	        MOVQ       16(SP), CX
	        PCDATA     $0, $3
	        MOVQ       CX, _r2+80(SP)
	        PCDATA     $2, $0
	        MOVQ       AX, _r2+88(SP)
	        // MOVQ    32(SP), BP (BP restore)
	        // ADDQ    $40, SP (SP restore)
	        RET
	pc130:											<-- slow path (tracepoint attached)
	        PCDATA     $2, $1             // ztrace.go:51
	        PCDATA     $0, $0
	        MOVQ       link+48(SP), AX
	        PCDATA     $2, $0
	        MOVQ       AX, (SP)
	        MOVL       connId+56(SP), CX
	        MOVL       CX, 8(SP)
	        MOVQ       msg+64(SP), DX
	        MOVQ       DX, 16(SP)
	        PCDATA     $2, $3
	        MOVQ       msg+72(SP), BX
	        PCDATA     $2, $0
	        MOVQ       BX, 24(SP)
	        CALL       lab·nexedi·com∕kirr∕neo∕go∕neo∕neonet·_traceMsgSendPre_run(SB)
	        JMP        pc44
	        // NOP (stack growth)
	        // PCDATA  $0, $-1            // connection.go:1368
	        // PCDATA  $2, $-1
	        // CALL    runtime.morestack_noctxt(SB)
	        // JMP     0

This continues b46436bd (tracing/runtime: Try to add support for Go1.12):

Move `+build ...` constraint in assembly files to the top, as suggested
by Russ Cox:

	https://github.com/golang/go/issues/31410#issuecomment-482599134

Then go stops complaining about it.

The build constraint had no effect previously, but it was not caught
because getg is used only on race builds and I was testing on amd64
only, which is practically almost the only ISA supported by race
detector as of Go1.11 .

Generate g for Go 1.12; no changes here compared to Go 1.11, however
go1.12 build build fails because of +build in .s file:

	# lab.nexedi.com/kirr/go123/tracing/internal/xruntime
	./runtime_g_amd64.s:3:1: +build comment must appear before package clause and be followed by a blank line

Build problem reported upstream:

	https://github.com/golang/go/issues/31410

Pygolang, starting from 0.0.0.dev8, deprecates @method(cls) in favour of @func(cls):

	pygolang@942ee900

- sqliteutil moved to -> sqlitex (https://github.com/crawshaw/sqlite/commit/e68ccf033b)
- Poll moved from sqlite to sqlitex (https://github.com/crawshaw/sqlite/commit/1967107395)
- Poll now takes full context, not only done channel (https://github.com/crawshaw/sqlite/commit/93b88b3c5c)

To -> pygolang@32a21d5b

Pygolang, starting from 0.0.0.dev5 provides working defer.

We will hopefully need it in the future to test external python code
similarly to when testing in-process go code with the help of
tracepoints. See module description for details (tracetest is not yet
done).

There is no yet Go client API for interacting with such-traced python
program. For the record: manually inspecting traced python process could
be done via e.g.

	socat EXEC:"./pyruntraced 3 neo.trace.py -- ../../../t/backup-play/N1-writer",fdin=3,fdout=3 TCP:localhost:8888

and telnetting to localhost:8888 from another xterm.

This patch brings lonet implementation in Python with the idea that Go
and Python programs could interoperate via lonet network and thus mixed
Go/Python application cluster could be tested.

Implementation quality is lower compared to Go version, but still it
should be more or less ok.