logdog: Add bundler library.

client/internal/logdog/butler/bundler/stream.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 (
+        "sync"
+        "sync/atomic"
+        "time"
+
+        "github.com/luci/luci-go/common/logdog/protocol"
+)
+
+var (
+        // dataBufferSize is the size (in bytes) of the Data objects that a Stream
+        // will lease.
+        dataBufferSize = 4096
+)
+
+// Stream is an individual Bundler Stream. Data is added to the Stream as a
+// series of ordered binary chunks.
+//
+// A Stream is not goroutine-safe.
+type Stream interface {
+        // LeaseData allocates and returns a Data block that stream data can be
+        // loaded into. The caller should Release() the Data, or transfer ownership to
+        // something that will (e.g., Append()).
+        LeaseData() Data
+
+        // Append adds a sequential chunk of data to the Stream. Append may block if
+        // the data isn't ready to be consumed.
+        //
+        // Append takes possession of the supplied Data, and will Release it when
+        // finished.
+        Append(Data) error
+
+        // Close closes the Stream, flushing any remaining data.
+        Close()
+}
+
+// streamConfig is the set of static configuration parameters for the stream.
+type streamConfig struct {
+        // name is the name of this stream.
+        name string
+
+        // parser is the stream parser to use.
+        parser parser
+
+        // maximumBufferedBytes is the maximum number of bytes that this stream will
+        // retain in its parser before blocking subsequent Append attempts.
+        maximumBufferedBytes int64
+        // maximumBufferDuration is the maximum amount of time that a block of data
+        // can be comfortably buffered in the stream.
+        maximumBufferDuration time.Duration
+
+        // template is the minimally-populated Butler log bundle entry.
+        template protocol.ButlerLogBundle_Entry
+
+        // onAppend, if not nil, is invoked when an attempt to append data to the
+        // stream occurs. If true is passed, the data was successfully appended. If
+        // false was passed, the data could not be appended immediately and the stream
+        // will block pending data consumption.
+        //
+        // The stream's append lock will be held when this method is called.
+        onAppend func(bool)
+}
+
+// streamImpl is a Stream implementation that is bound to a Bundler.
+type streamImpl struct {
+        c *streamConfig
+
+        // drained is true if the stream is finished emitting data.
+        //
+        // It is an atomic value, with zero indicating not drained and non-zero
+        // indicating drained. It should be accessed via isDrained, and set with
+        // setDrained.
+        drained int32
+
+        // parserLock is a Mutex protecting the stream's parser instance and its
+        // underlying chunk.Buffer. Any access to either of these fields must be done
+        // while holding this lock.
+        parserLock sync.Mutex
+
+        // dataConsumedSignalC is a channel that can be used to signal when data has
+        // been consumed. It is set via signalDataConsumed.
+        dataConsumedSignalC chan struct{}
+        // appendErrValue is an atomically-set error. It will be returned by Append if
+        // an error occurs during stream processing.
+        appendErrValue atomic.Value
+
+        // stateLock protects stream state against concurrent access.
+        stateLock sync.Mutex
+        // closed, if non-zero, indicates that we have been closed and our stream has
+        // finished reading.
+        //
+        // stateLock must be held when accessing this field.
+        closed bool
+        // lastLogEntry is a pointer to the last LogEntry that was exported.
+        //
+        // stateLock must be held when accessing this field.
+        lastLogEntry *protocol.LogEntry
+
+        // testAppendWaitCallback, if not nil, is called before Append blocks.
+        // This callback is used for testing coordination.
+        testAppendWaitCallback func()
+}
+
+func newStream(c streamConfig) *streamImpl {
+        return &streamImpl{
+                c: &c,
+
+                dataConsumedSignalC: make(chan struct{}, 1),
+        }
+}
+
+func (s *streamImpl) LeaseData() Data {
+        return globalDataPoolRegistry.getPool(dataBufferSize).getData()
+}
+
+func (s *streamImpl) Append(d Data) error {
+        defer func() {
+                if d != nil {
+                        d.Release()
+                }
+        }()
+
+        // Block/loop until we've successfully appended the data.
+        for {
+                if err := s.appendError(); err != nil || d.Len() == 0 {
+                        return err
+                }
+
+                s.withParserLock(func() {
+                        if s.c.parser.bufferedBytes() == 0 ||
+                                s.c.parser.bufferedBytes()+int64(d.Len()) <= s.c.maximumBufferedBytes {
+                                s.c.parser.appendData(d)
+                                d = nil
+                        }
+                })
+
+                // The data was appended; we're done.
+                if s.c.onAppend != nil {
+                        s.c.onAppend(d == nil)
+                }
+                if d == nil {
+                        break
+                }
+
+                // Not ready to append; wait for a data event and re-evaluate.
+                <-s.dataConsumedSignalC
+        }
+
+        return nil
+}
+
+// Signals our Append loop that data has been consumed.
+func (s *streamImpl) signalDataConsumed() {
+        select {
+        case s.dataConsumedSignalC <- struct{}{}:
+                break
+
+        default:
+                break
+        }
+}
+
+func (s *streamImpl) Close() {
+        s.stateLock.Lock()
+        defer s.stateLock.Unlock()
+
+        s.closed = true
+        s.maybeSetDrainedLocked()
+}
+
+func (s *streamImpl) name() string {
+        return s.c.name
+}
+
+// isDrained returns true if this stream is finished emitting data.
+//
+// This can happen if either:
+// - The stream is closed and has no more buffered data, or
+// - The strema has encountered a fatal error during processing.
+func (s *streamImpl) isDrained() bool {
+        return atomic.LoadInt32(&s.drained) != 0
+}
+
+// setDrained marks this stream as drained.
+func (s *streamImpl) setDrained() {
+        atomic.StoreInt32(&s.drained, 1)
+}
+
+// maybeSetDrainedLocked evaluates our buffer stream status. If the stream is
+// closed and our buffer is empty, it will set the drained state to true.
+//
+// The stream's stateLock must be held when calling this method.
+//
+// The resulting drained state will be returned.
+func (s *streamImpl) maybeSetDrainedLocked() bool {
+        if s.isDrained() {
+                return true
+        }
+
+        // Not drained ... should we be?
+        if s.closed {
+                bufSize := int64(0)
+                s.withParserLock(func() {
+                        bufSize = s.c.parser.bufferedBytes()
+                })
+                if bufSize == 0 {
+                        s.setDrained()
+                        return true
+                }
+        }
+
+        return false
+}
+
+// expireTime returns the Time when the oldest chunk in the stream will expire.
+//
+// This is calculated ask:
+// oldest.Timestamp + stream.maximumBufferDuration
+// If there is no buffered data, oldest will return nil.
+func (s *streamImpl) expireTime() (t time.Time, has bool) {
+        s.withParserLock(func() {
+                t, has = s.c.parser.firstChunkTime()
+        })
+
+        if has {
+                t = t.Add(s.c.maximumBufferDuration)
+        }
+        return
+}
+
+// nextBundleEntry generates bundles for this stream. The total bundle data size
+// must not exceed the supplied size.
+//
+// If no bundle entry could be generated given the constraints, nil will be
+// returned.
+//
+// It is possible for some entries to be returned alongside an error.
+func (s *streamImpl) nextBundleEntry(bb *builder, aggressive bool) bool {
+        s.stateLock.Lock()
+        defer s.stateLock.Unlock()
+
+        // If we're not drained, try and get the next bundle.
+        modified := false
+        if !s.maybeSetDrainedLocked() {
+                err := error(nil)
+                modified, err = s.nextBundleEntryLocked(bb, aggressive)
+                if err != nil {
+                        s.setAppendError(err)
+                        s.setDrained()
+                }
+
+                if modified {
+                        s.signalDataConsumed()
+                }
+        }
+
+        // If we're drained, populate our terminal state.
+        if s.maybeSetDrainedLocked() && s.lastLogEntry != nil {
+                bb.setStreamTerminal(&s.c.template, s.lastLogEntry.StreamIndex)
+        }
+
+        return modified
+}
+
+func (s *streamImpl) nextBundleEntryLocked(bb *builder, aggressive bool) (bool, error) {
+        c := constraints{
+                truncate: aggressive,
+                closed:   s.closed,
+        }
+
+        // Extract as many entries as possible from the stream. As we extract, adjust
+        // our byte size.
+        //
+        // If we're closed, this will continue to consume until finished. If an error
+        // occurs, shut down data collection.
+        modified := false
+        ierr := error(nil)
+
+        for c.limit = bb.remaining(); c.limit > 0; c.limit = bb.remaining() {
+                emittedLog := false
+                s.withParserLock(func() {
+                        le, err := s.c.parser.nextEntry(&c)
+                        if err != nil {
+                                ierr = err
+                                return
+                        }
+
+                        if le == nil {
+                                return
+                        }
+
+                        emittedLog = true
+                        modified = true
+                        s.lastLogEntry = le
+                        bb.add(&s.c.template, le)
+                })
+
+                if !emittedLog {
+                        break
+                }
+        }
+
+        return modified, ierr
+}
+
+func (s *streamImpl) withParserLock(f func()) {
+        s.parserLock.Lock()
+        defer s.parserLock.Unlock()
+
+        f()
+}
+
+func (s *streamImpl) appendError() error {
+        if err := s.appendErrValue.Load(); err != nil {
+                return err.(error)
+        }
+        return nil
+}
+
+func (s *streamImpl) setAppendError(err error) {
+        s.appendErrValue.Store(err)
+        s.signalDataConsumed()
+}