Project import generated by Copybara.
PiperOrigin-RevId: 229942388
Change-Id: Ib5a23c152c95ed4294cece9f902227c21ce531ef
diff --git a/spdy/core/write_scheduler.h b/spdy/core/write_scheduler.h
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+// Copyright (c) 2016 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.
+
+#ifndef QUICHE_SPDY_CORE_WRITE_SCHEDULER_H_
+#define QUICHE_SPDY_CORE_WRITE_SCHEDULER_H_
+
+#include <cstdint>
+#include <tuple>
+#include <vector>
+
+#include "net/third_party/quiche/src/spdy/core/spdy_protocol.h"
+#include "net/third_party/quiche/src/spdy/platform/api/spdy_export.h"
+#include "net/third_party/quiche/src/spdy/platform/api/spdy_string.h"
+
+namespace spdy {
+
+// Abstract superclass for classes that decide which SPDY or HTTP/2 stream to
+// write next. Concrete subclasses implement various scheduling policies:
+//
+// PriorityWriteScheduler: implements SPDY priority-based stream scheduling,
+// where (writable) higher-priority streams are always given precedence
+// over lower-priority streams.
+//
+// Http2PriorityWriteScheduler: implements SPDY priority-based stream
+// scheduling coupled with the HTTP/2 stream dependency model. This is only
+// intended as a transitional step towards Http2WeightedWriteScheduler.
+//
+// Http2WeightedWriteScheduler (coming soon): implements the HTTP/2 stream
+// dependency model with weighted stream scheduling, fully conforming to
+// RFC 7540.
+//
+// The type used to represent stream IDs (StreamIdType) is templated in order
+// to allow for use by both SPDY and QUIC codebases. It must be a POD that
+// supports comparison (i.e., a numeric type).
+//
+// Each stream can be in one of two states: ready or not ready (for writing).
+// Ready state is changed by calling the MarkStreamReady() and
+// MarkStreamNotReady() methods. Only streams in the ready state can be
+// returned by PopNextReadyStream(); when returned by that method, the stream's
+// state changes to not ready.
+template <typename StreamIdType>
+class SPDY_EXPORT_PRIVATE WriteScheduler {
+ public:
+ typedef StreamPrecedence<StreamIdType> StreamPrecedenceType;
+
+ virtual ~WriteScheduler() {}
+
+ // Registers new stream |stream_id| with the scheduler, assigning it the
+ // given precedence. If the scheduler supports stream dependencies, the
+ // stream is inserted into the dependency tree under
+ // |precedence.parent_id()|.
+ //
+ // Preconditions: |stream_id| should be unregistered, and
+ // |precedence.parent_id()| should be registered or |kHttp2RootStreamId|.
+ virtual void RegisterStream(StreamIdType stream_id,
+ const StreamPrecedenceType& precedence) = 0;
+
+ // Unregisters the given stream from the scheduler, which will no longer keep
+ // state for it.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual void UnregisterStream(StreamIdType stream_id) = 0;
+
+ // Returns true if the given stream is currently registered.
+ virtual bool StreamRegistered(StreamIdType stream_id) const = 0;
+
+ // Returns the precedence of the specified stream. If the scheduler supports
+ // stream dependencies, calling |parent_id()| on the return value returns the
+ // stream's parent, and calling |exclusive()| returns true iff the specified
+ // stream is an only child of the parent stream.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual StreamPrecedenceType GetStreamPrecedence(
+ StreamIdType stream_id) const = 0;
+
+ // Updates the precedence of the given stream. If the scheduler supports
+ // stream dependencies, |stream_id|'s parent will be updated to be
+ // |precedence.parent_id()| if it is not already.
+ //
+ // Preconditions: |stream_id| should be unregistered, and
+ // |precedence.parent_id()| should be registered or |kHttp2RootStreamId|.
+ virtual void UpdateStreamPrecedence(
+ StreamIdType stream_id,
+ const StreamPrecedenceType& precedence) = 0;
+
+ // Returns child streams of the given stream, if any. If the scheduler
+ // doesn't support stream dependencies, returns an empty vector.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual std::vector<StreamIdType> GetStreamChildren(
+ StreamIdType stream_id) const = 0;
+
+ // Records time (in microseconds) of a read/write event for the given
+ // stream.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual void RecordStreamEventTime(StreamIdType stream_id,
+ int64_t now_in_usec) = 0;
+
+ // Returns time (in microseconds) of the last read/write event for a stream
+ // with higher priority than the priority of the given stream, or 0 if there
+ // is no such event.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual int64_t GetLatestEventWithPrecedence(
+ StreamIdType stream_id) const = 0;
+
+ // If the scheduler has any ready streams, returns the next scheduled
+ // ready stream, in the process transitioning the stream from ready to not
+ // ready.
+ //
+ // Preconditions: |HasReadyStreams() == true|
+ virtual StreamIdType PopNextReadyStream() = 0;
+
+ // If the scheduler has any ready streams, returns the next scheduled
+ // ready stream and its priority, in the process transitioning the stream from
+ // ready to not ready.
+ //
+ // Preconditions: |HasReadyStreams() == true|
+ virtual std::tuple<StreamIdType, StreamPrecedenceType>
+ PopNextReadyStreamAndPrecedence() = 0;
+
+ // Returns true if there's another stream ahead of the given stream in the
+ // scheduling queue. This function can be called to see if the given stream
+ // should yield work to another stream.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual bool ShouldYield(StreamIdType stream_id) const = 0;
+
+ // Marks the stream as ready to write. If the stream was already ready, does
+ // nothing. If add_to_front is true, the stream is scheduled ahead of other
+ // streams of the same priority/weight, otherwise it is scheduled behind them.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual void MarkStreamReady(StreamIdType stream_id, bool add_to_front) = 0;
+
+ // Marks the stream as not ready to write. If the stream is not registered or
+ // not ready, does nothing.
+ //
+ // Preconditions: |stream_id| should be registered.
+ virtual void MarkStreamNotReady(StreamIdType stream_id) = 0;
+
+ // Returns true iff the scheduler has any ready streams.
+ virtual bool HasReadyStreams() const = 0;
+
+ // Returns the number of streams currently marked ready.
+ virtual size_t NumReadyStreams() const = 0;
+
+ // Returns summary of internal state, for logging/debugging.
+ virtual SpdyString DebugString() const = 0;
+};
+
+} // namespace spdy
+
+#endif // QUICHE_SPDY_CORE_WRITE_SCHEDULER_H_
