logdog: Add bundler library.

client/internal/logdog/butler/bundler/bundler_impl.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package bundler
+
+import (
+        "sort"
+
+        "github.com/luci/luci-go/common/logdog/protocol"
+        "github.com/luci/luci-go/common/logdog/protocol/protoutil"

[tandrii(chromium), 2015/08/11 14:06:07]

i think you have CL on which this one depends, but somehow I don't see it
mentioned (2+weeks old "git cl upload" does it automatically).

[dnj (Google), 2015/08/11 16:24:01]

https://codereview.chromium.org/1272893004

+        "github.com/luci/luci-go/common/logdog/types"
+)
+
+type bundlerStream struct {

[tandrii(chromium), 2015/08/11 14:06:07]

this isn't used in this CL.

[dnj (Google), 2015/08/11 16:24:01]

Hm? It's used all over the place in this file.

[tandrii(chromium), 2015/08/11 17:32:22]

sorry, that was meant for a different line, and even there it was wrong.

+        entry *protocol.ButlerLogBundle_Entry
+        logs  []*protocol.LogEntry
+}
+
+func (s *bundlerStream) mergeEntry(e *protocol.ButlerLogBundle_Entry) {
+        if e.GetTerminal() && !s.entry.GetTerminal() {
+                s.entry.Terminal = e.Terminal
+                s.entry.TerminalIndex = e.TerminalIndex
+        }
+}
+
+// bundlerImpl is an implementation of the Bundler interface.
+type bundlerImpl struct {
+        *Config
+
+        sizer   Sizer
+        bundle  *protocol.ButlerLogBundle
+        entries map[types.StreamPath]*bundlerStream
+        count   int
+}
+
+// New instantiates a new Bundler instance.
+func New(c Config) Bundler {

[tandrii(chromium), 2015/08/11 14:06:07]

Why pass config as a copy if you take a ref to it anyways? Given that Config is
very small struct, i'd pass it as a copy everywhere.

[dnj (Google), 2015/08/11 16:24:01]

No point. This function owns this instance of Config, so  might as well just ref
it. It's a good pattern, moreso when Config is larger but here too.

[tandrii(chromium), 2015/08/11 17:32:22]

sorry, my comment was stupid because I didn't quite capture that you embed
Config into bundlerImpl. The right question is why not "func New(c *Config)
Bundler {"

[dnj, 2015/08/11 18:14:27]

In the end it would have the same effect. However, by not using a reference in
the function signature, it's very clear to the caller that the configuration
will be copied.

[tandrii(chromium), 2015/08/11 18:31:05]

Acknowledged.

+        b := &bundlerImpl{
+                Config:  &c,
+                bundle:  &protocol.ButlerLogBundle{},
+                entries: make(map[types.StreamPath]*bundlerStream),

[tandrii(chromium), 2015/08/11 14:06:07]

nit: map[types.StreamPath]*bundlerStream{}

[dnj (Google), 2015/08/11 16:24:01]

*sigh* Any idea why we seem to be shying away from perfectly normal
initializers? Done.

[tandrii(chromium), 2015/08/11 17:32:22]

hm, don't you still need an instance of bundle? It currently is nil.

[dnj, 2015/08/11 18:14:27]

"bundle" has been replaced with "Config.TemplateBundle".

[tandrii(chromium), 2015/08/11 18:31:05]

ah, not in PS2, though. In PS3 -> ok :)

[dnj (Google), 2015/08/12 03:20:09]

Well, not used in PS2, properly removed in PS3 :)

+        }
+        b.reset()
+        return b
+}
+
+func (b *bundlerImpl) Append(e *protocol.ButlerLogBundle_Entry) {
+        // Take ownership of the entry's logs.
+        logs := e.GetLogs()
+        e.Logs = nil
+
+        // Ignore bundle entries that don't contribute to the log stream's
+        // advancement.
+        if !(len(logs) > 0 || e.GetTerminal()) {
+                return
+        }
+
+        // Add this log to our reserve.
+        path := protoutil.DescriptorPath(e.GetDesc())
+        cur, ok := b.entries[path]
+        if !ok {
+                // Add this new entry to the bundle.
+                b.sizer.AppendBundleEntry(e)
+                cur = &bundlerStream{
+                        entry: e,
+                        logs:  make([]*protocol.LogEntry, 0, len(logs)),
+                }
+                b.entries[path] = cur
+        } else {
+                cur.mergeEntry(e)
+        }
+
+        for _, le := range logs {
+                b.sizer.AppendLogEntry(e, le)
+        }
+        cur.logs = append(cur.logs, logs...)
+        b.count += len(logs)
+        return
+}
+
+func (b *bundlerImpl) reset() {
+        b.sizer = b.newSizer(b.bundle)
+        b.count = 0

[tandrii(chromium), 2015/08/11 14:06:07]

shouldn't this also reset the entries?

[dnj (Google), 2015/08/11 16:24:01]

The idea was that "GetBundles" will consume all bundles in "entries", implicitly
clearing it. However, there is an edge case (threshold is too small to consume
any bundle) that I wasn't taking in to account, so I'll clear it here.

[tandrii(chromium), 2015/08/11 17:32:22]

Acknowledged.

+}
+
+func (b *bundlerImpl) Empty() bool {
+        return len(b.entries) == 0
+}
+
+func (b *bundlerImpl) Size() int {
+        return b.sizer.Size()
+}
+
+func (b *bundlerImpl) GetBundles(threshold int) []*protocol.ButlerLogBundle {
+        b.reset()
+
+        bundles := []*protocol.ButlerLogBundle(nil)
+        for {
+                bundle := b.getNextBundle(threshold)
+                if bundle == nil {
+                        return bundles
+                }
+                bundles = append(bundles, bundle)
+        }
+}
+
+func (b *bundlerImpl) getNextBundle(threshold int) *protocol.ButlerLogBundle {
+        // Populate the bundle with as many entries as possible.
+        bundle := *b.bundle

[tandrii(chromium), 2015/08/11 14:06:07]

i'd add comment here that you really want to copy bundle.

[dnj (Google), 2015/08/11 16:24:01]

Done.

+        bundle.Entries = append([]*protocol.ButlerLogBundle_Entry(nil), bundle.Entries...)

[tandrii(chromium), 2015/08/11 14:06:07]

I don't understand why you copy bundle entries here. On line #136 you append
essentially a copy, possibly modified, of the entry which is already in this
list. So, maybe you intended to just create new slice here?

Also, why []*protocol.ButlerLogBundle_Entry(nil) and not
[]*protocol.ButlerLogBundle_Entry{} ? Is this to avoid extra slice memory
allocation?

Cryptic but neat replacement for ugly copy command :)

[dnj (Google), 2015/08/11 16:24:01]

Originally it was to hedge the case where the template bundle had existing log
entries. I was overthinking it, though. I've updated the code: template
bundle/bundle-entry will never have logs, no need to accommodate that.
Heh thanks :)

+        sizer := b.newSizer(&bundle)

[tandrii(chromium), 2015/08/11 14:06:07]

nit: i'd move this line closer to overThreshold func (line #120)

[dnj (Google), 2015/08/11 16:24:01]

Done.

+
+        // For determinism, add buffered entries in order of path.
+        keys := make([]string, 0, len(b.entries))
+        for k := range b.entries {
+                keys = append(keys, string(k))
+        }
+        sort.Sort(sort.StringSlice(keys))

[tandrii(chromium), 2015/08/11 14:06:07]

just sort.Strings(keys)
https://golang.org/pkg/sort/#Strings

[dnj (Google), 2015/08/11 16:24:01]

Done.

+
+        overThreshold := func() bool {
+                return threshold != 0 && threshold < sizer.Size()
+        }
+
+BuildLoop:
+        for _, k := range keys {
+                e := b.entries[types.StreamPath(k)]
+
+                // Can we add this entry without exceeding our size threshold?

[tandrii(chromium), 2015/08/11 14:06:07]

what if threshold is small enough that the number of possible entries is 0?
Given overestimation of fastSizer and I claim it could happen. Then, how do we
ensure progress of our system?

Do you argue that's super unlikely because threshold will always be at least say
1MB?

[dnj (Google), 2015/08/11 16:24:01]

It's allowed to happen. In that case, we will just drop log messages. I'll
update comments/code to reflect this and add test cases.

In practice it won't, because the single place that this is used will never have
such a low constraint, but it would be a nasty surprise not to accommodate it.

+                sizer.AppendBundleEntry(e.entry)
+                if overThreshold() {
+                        break BuildLoop
+                }
+                ec := *e.entry
+                ec.Logs = append([]*protocol.LogEntry(nil), ec.Logs...)

[tandrii(chromium), 2015/08/11 14:06:07]

same as line #111: why copy ec.Logs here if you essentially append them one by
one below?

[dnj (Google), 2015/08/11 16:24:01]

Don't anymore; mandatory "nil" assumption.

+                bundle.Entries = append(bundle.Entries, &ec)
+
+                for i, le := range e.logs {
+                        sizer.AppendLogEntry(e.entry, le)
+
+                        if overThreshold() {
+                                e.logs = append(e.logs[:0], e.logs[i:]...)

[tandrii(chromium), 2015/08/11 14:06:07]

My test http://play.golang.org/p/g0387lE-R7 sort of says it works (see array c
and how it modified a). Neat.

However, append() doesn't guarantee that it moves elements one by one and in
order, at least not in docs. So, maybe it's better to play safe and just
allocate new memory? Or, if not allocate, then roll your own for loop.

[dnj (Google), 2015/08/11 16:24:01]

Good thought!  However, from here, it does say that append is allowed to
overlap:
http://golang.org/ref/spec#Appending_and_copying_slices

[tandrii(chromium), 2015/08/11 17:32:22]

Déjà vu: I knew I saw it somewhere, but yet again couldn't find it easily (who
checks second link in Google search anyway?). Thanks!

[dnj, 2015/08/11 18:14:27]

No worries, it took me a bit of digging to find, so it was hardly obvious. Maybe
Go should, you know, add this to the "append" function's documentation or
something...

+                                break BuildLoop
+                        }
+                        ec.Logs = append(ec.Logs, le)
+                }
+
+                // This entry has been fully added.
+                delete(b.entries, types.StreamPath(k))
+        }
+
+        if len(bundle.Entries) == 0 {
+                return nil
+        }
+        return &bundle
+}
+
+func (b *bundlerImpl) newSizer(bundle *protocol.ButlerLogBundle) Sizer {
+        nb := b.NewSizer
+        if nb == nil {
+                nb = NewFastSizer
+        }
+        return nb(bundle)
+}