Update mojo sdk to rev 3d23dae011859a2aae49f1d1adde705c8e85d819

third_party/mojo/src/mojo/public/go/bindings/async_waiter.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 bindings
+
+import (
+        "fmt"
+        "sync"
+        "sync/atomic"
+
+        "mojo/public/go/system"
+)
+
+var waiter *asyncWaiterImpl
+var once sync.Once
+
+// GetAsyncWaiter returns a default implementation of |AsyncWaiter| interface.
+func GetAsyncWaiter() AsyncWaiter {
+        once.Do(func() {
+                waiter = newAsyncWaiter()
+        })
+        return waiter
+}
+
+// AsyncWaitId is an id returned by |AsyncWait()| used to cancel it.
+type AsyncWaitId uint64
+
+// WaitResponse is a struct sent to a channel waiting for |AsyncWait()| to
+// finish. It contains the same information as if |Wait()| was called on a
+// handle.
+type WaitResponse struct {
+        Result system.MojoResult
+        State  system.MojoHandleSignalsState
+}
+
+// AsyncWaiter defines an interface for asynchronously waiting (and cancelling
+// asynchronous waits) on a handle.
+type AsyncWaiter interface {
+        // AsyncWait asynchronously waits on a given handle until a signal
+        // indicated by |signals| is satisfied or it becomes known that no
+        // signal indicated by |signals| will ever be satisified. The wait
+        // response will be sent to |responseChan|.
+        //
+        // |handle| must not be closed or transferred until the wait response
+        // is received from |responseChan|.
+        AsyncWait(handle system.Handle, signals system.MojoHandleSignals, responseChan chan<- WaitResponse) AsyncWaitId
+
+        // CancelWait cancels an outstanding async wait (specified by |id|)
+        // initiated by |AsyncWait()|. A response with Mojo result
+        // |MOJO_RESULT_ABORTED| is sent to the corresponding |responseChan|.
+        CancelWait(id AsyncWaitId)
+}
+
+// waitRequest is a struct sent to asyncWaiterWorker to add another handle to
+// the list of waiting handles.
+type waitRequest struct {
+        handle  system.Handle
+        signals system.MojoHandleSignals
+
+        // Used for |CancelWait()| calls. The worker should issue IDs so that
+        // you can't cancel the wait until the worker received the wait request.
+        idChan chan<- AsyncWaitId
+
+        // A channel end to send wait results.
+        responseChan chan<- WaitResponse
+}
+
+// asyncWaiterWorker does the actual work, in its own goroutine. It calls
+// |WaitMany()| on all provided handles. New handles a added via |waitChan|
+// and removed via |cancelChan| messages. To wake the worker asyncWaiterImpl
+// sends mojo messages to a dedicated message pipe, the other end of which has
+// index 0 in all slices of the worker.
+type asyncWaiterWorker struct {
+        // |handles| and |signals| are used to make |WaitMany()| calls directly.
+        // All these arrays should be operated simultaneously; i-th element
+        // of each refers to i-th handle.
+        handles      []system.Handle
+        signals      []system.MojoHandleSignals
+        asyncWaitIds []AsyncWaitId
+        responses    []chan<- WaitResponse
+
+        // Flag shared between waiterImpl and worker that is 1 iff the worker is
+        // already notified by waiterImpl. The worker sets it to 0 as soon as
+        // |WaitMany()| succeeds.
+        isNotified *int32
+        waitChan   <-chan waitRequest // should have a non-empty buffer
+        cancelChan <-chan AsyncWaitId // should have a non-empty buffer
+        lastUsedId AsyncWaitId        // is incremented each |AsyncWait()| call
+}
+
+// removeHandle removes handle at provided index without sending response by
+// swapping all information associated with index-th handle with the last one
+// and removing the last one.
+func (w *asyncWaiterWorker) removeHandle(index int) {
+        l := len(w.handles) - 1
+        // Swap with the last and remove last.
+        w.handles[index] = w.handles[l]
+        w.handles = w.handles[0:l]
+        w.signals[index] = w.signals[l]
+        w.signals = w.signals[0:l]
+
+        w.asyncWaitIds[index] = w.asyncWaitIds[l]
+        w.asyncWaitIds = w.asyncWaitIds[0:l]
+        w.responses[index] = w.responses[l]
+        w.responses = w.responses[0:l]
+}
+
+// sendWaitResponseAndRemove send response to corresponding channel and removes
+// index-th waiting handle.
+func (w *asyncWaiterWorker) sendWaitResponseAndRemove(index int, result system.MojoResult, state system.MojoHandleSignalsState) {
+        w.responses[index] <- WaitResponse{
+                result,
+                state,
+        }
+        w.removeHandle(index)
+}
+
+// respondToSatisfiedWaits responds to all wait requests that have at least
+// one satisfied signal and removes them.
+func (w *asyncWaiterWorker) respondToSatisfiedWaits(states []system.MojoHandleSignalsState) {
+        // Don't touch handle at index 0 as it is the waking handle.
+        for i := 1; i < len(states); {
+                if (states[i].SatisfiedSignals & w.signals[i]) != 0 {
+                        // Respond and swap i-th with last and remove last.
+                        w.sendWaitResponseAndRemove(i, system.MOJO_RESULT_OK, states[i])
+                        // Swap i-th with last and remove last.
+                        states[i] = states[len(states)-1]
+                        states = states[:len(states)-1]
+                } else {
+                        i++
+                }
+        }
+}
+
+// processIncomingRequests processes all queued async wait or cancel requests
+// sent by asyncWaiterImpl.
+func (w *asyncWaiterWorker) processIncomingRequests() {
+        for {
+                select {
+                case request := <-w.waitChan:
+                        w.handles = append(w.handles, request.handle)
+                        w.signals = append(w.signals, request.signals)
+                        w.responses = append(w.responses, request.responseChan)
+
+                        w.lastUsedId++
+                        id := w.lastUsedId
+                        w.asyncWaitIds = append(w.asyncWaitIds, id)
+                        request.idChan <- id
+                case AsyncWaitId := <-w.cancelChan:
+                        // Zero index is reserved for the waking message pipe handle.
+                        index := 0
+                        for i := 1; i < len(w.asyncWaitIds); i++ {
+                                if w.asyncWaitIds[i] == AsyncWaitId {
+                                        index = i
+                                        break
+                                }
+                        }
+                        // Do nothing if the id was not found as wait response may be
+                        // already sent if the async wait was successful.
+                        if index > 0 {
+                                w.sendWaitResponseAndRemove(index, system.MOJO_RESULT_ABORTED, system.MojoHandleSignalsState{})
+                        }
+                default:
+                        return
+                }
+        }
+}
+
+// runLoop run loop of the asyncWaiterWorker. Blocks on |WaitMany()|. If the
+// wait is interrupted by waking handle (index 0) then it means that the worker
+// was woken by waiterImpl, so the worker processes incoming requests from
+// waiterImpl; otherwise responses to corresponding wait request.
+func (w *asyncWaiterWorker) runLoop() {
+        for {
+                result, index, states := system.GetCore().WaitMany(w.handles, w.signals, system.MOJO_DEADLINE_INDEFINITE)
+                // Set flag to 0, so that the next incoming request to
+                // waiterImpl would explicitly wake worker by sending a message
+                // to waking message pipe.
+                atomic.StoreInt32(w.isNotified, 0)
+                if index == -1 {
+                        panic(fmt.Sprintf("error waiting on handles: %v", result))
+                        break
+                }
+                // Zero index means that the worker was signaled by asyncWaiterImpl.
+                if index == 0 {
+                        if result != system.MOJO_RESULT_OK {
+                                panic(fmt.Sprintf("error waiting on waking handle: %v", result))
+                        }
+                        w.handles[0].(system.MessagePipeHandle).ReadMessage(system.MOJO_READ_MESSAGE_FLAG_NONE)
+                        w.processIncomingRequests()
+                } else if result != system.MOJO_RESULT_OK {
+                        w.sendWaitResponseAndRemove(index, result, system.MojoHandleSignalsState{})
+                } else {
+                        w.respondToSatisfiedWaits(states)
+                }
+        }
+}
+
+// asyncWaiterImpl is an implementation of |AsyncWaiter| interface.
+// Runs a worker in a separate goroutine and comunicates with it by sending a
+// message to |wakingHandle| to wake worker from |WaitMany()| call and
+// sending request via |waitChan| and |cancelChan|.
+type asyncWaiterImpl struct {
+        wakingHandle system.MessagePipeHandle
+
+        // Flag shared between waiterImpl and worker that is 1 iff the worker is
+        // already notified by waiterImpl. The worker sets it to 0 as soon as
+        // |WaitMany()| succeeds.
+        isWorkerNotified *int32
+        waitChan         chan<- waitRequest // should have a non-empty buffer
+        cancelChan       chan<- AsyncWaitId // should have a non-empty buffer
+}
+
+// newAsyncWaiter creates an asyncWaiterImpl and starts its worker goroutine.
+func newAsyncWaiter() *asyncWaiterImpl {
+        result, h0, h1 := system.GetCore().CreateMessagePipe(nil)
+        if result != system.MOJO_RESULT_OK {
+                panic(fmt.Sprintf("can't create message pipe %v", result))
+        }
+        waitChan := make(chan waitRequest, 10)
+        cancelChan := make(chan AsyncWaitId, 10)
+        isNotified := new(int32)
+        worker := asyncWaiterWorker{
+                []system.Handle{h1},
+                []system.MojoHandleSignals{system.MOJO_HANDLE_SIGNAL_READABLE},
+                []AsyncWaitId{0},
+                []chan<- WaitResponse{make(chan WaitResponse)},
+                isNotified,
+                waitChan,
+                cancelChan,
+                0,
+        }
+        go worker.runLoop()
+        return &asyncWaiterImpl{
+                wakingHandle:     h0,
+                isWorkerNotified: isNotified,
+                waitChan:         waitChan,
+                cancelChan:       cancelChan,
+        }
+}
+
+// wakeWorker wakes the worker from |WaitMany()| call. This should be called
+// after sending a message to |waitChan| or |cancelChan| to avoid deadlock.
+func (w *asyncWaiterImpl) wakeWorker() {
+        if atomic.CompareAndSwapInt32(w.isWorkerNotified, 0, 1) {
+                w.wakingHandle.WriteMessage([]byte{0}, nil, system.MOJO_WRITE_MESSAGE_FLAG_NONE)
+        }
+}
+
+func (w *asyncWaiterImpl) AsyncWait(handle system.Handle, signals system.MojoHandleSignals, responseChan chan<- WaitResponse) AsyncWaitId {
+        idChan := make(chan AsyncWaitId, 1)
+        w.waitChan <- waitRequest{
+                handle,
+                signals,
+                idChan,
+                responseChan,
+        }
+        w.wakeWorker()
+        return <-idChan
+}
+
+func (w *asyncWaiterImpl) CancelWait(id AsyncWaitId) {
+        w.cancelChan <- id
+        w.wakeWorker()
+}