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/*
*
* Copyright 2014 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package transport
import (
"fmt"
"math"
"sync"
"sync/atomic"
)
// writeQuota is a soft limit on the amount of data a stream can
// schedule before some of it is written out.
type writeQuota struct {
quota int32
// get waits on read from when quota goes less than or equal to zero.
// replenish writes on it when quota goes positive again.
ch chan struct{}
// done is triggered in error case.
done <-chan struct{}
// replenish is called by loopyWriter to give quota back to.
// It is implemented as a field so that it can be updated
// by tests.
replenish func(n int)
}
func newWriteQuota(sz int32, done <-chan struct{}) *writeQuota {
w := &writeQuota{
quota: sz,
ch: make(chan struct{}, 1),
done: done,
}
w.replenish = w.realReplenish
return w
}
func (w *writeQuota) get(sz int32) error {
for {
if atomic.LoadInt32(&w.quota) > 0 {
atomic.AddInt32(&w.quota, -sz)
return nil
}
select {
case <-w.ch:
continue
case <-w.done:
return errStreamDone
}
}
}
func (w *writeQuota) realReplenish(n int) {
sz := int32(n)
a := atomic.AddInt32(&w.quota, sz)
b := a - sz
if b <= 0 && a > 0 {
select {
case w.ch <- struct{}{}:
default:
}
}
}
type trInFlow struct {
limit uint32
unacked uint32
effectiveWindowSize uint32
}
func (f *trInFlow) newLimit(n uint32) uint32 {
d := n - f.limit
f.limit = n
f.updateEffectiveWindowSize()
return d
}
func (f *trInFlow) onData(n uint32) uint32 {
f.unacked += n
if f.unacked >= f.limit/4 {
w := f.unacked
f.unacked = 0
f.updateEffectiveWindowSize()
return w
}
f.updateEffectiveWindowSize()
return 0
}
func (f *trInFlow) reset() uint32 {
w := f.unacked
f.unacked = 0
f.updateEffectiveWindowSize()
return w
}
func (f *trInFlow) updateEffectiveWindowSize() {
atomic.StoreUint32(&f.effectiveWindowSize, f.limit-f.unacked)
}
func (f *trInFlow) getSize() uint32 {
return atomic.LoadUint32(&f.effectiveWindowSize)
}
// TODO(mmukhi): Simplify this code.
// inFlow deals with inbound flow control
type inFlow struct {
mu sync.Mutex
// The inbound flow control limit for pending data.
limit uint32
// pendingData is the overall data which have been received but not been
// consumed by applications.
pendingData uint32
// The amount of data the application has consumed but grpc has not sent
// window update for them. Used to reduce window update frequency.
pendingUpdate uint32
// delta is the extra window update given by receiver when an application
// is reading data bigger in size than the inFlow limit.
delta uint32
}
// newLimit updates the inflow window to a new value n.
// It assumes that n is always greater than the old limit.
func (f *inFlow) newLimit(n uint32) {
f.mu.Lock()
f.limit = n
f.mu.Unlock()
}
func (f *inFlow) maybeAdjust(n uint32) uint32 {
if n > uint32(math.MaxInt32) {
n = uint32(math.MaxInt32)
}
f.mu.Lock()
defer f.mu.Unlock()
// estSenderQuota is the receiver's view of the maximum number of bytes the sender
// can send without a window update.
estSenderQuota := int32(f.limit - (f.pendingData + f.pendingUpdate))
// estUntransmittedData is the maximum number of bytes the sends might not have put
// on the wire yet. A value of 0 or less means that we have already received all or
// more bytes than the application is requesting to read.
estUntransmittedData := int32(n - f.pendingData) // Casting into int32 since it could be negative.
// This implies that unless we send a window update, the sender won't be able to send all the bytes
// for this message. Therefore we must send an update over the limit since there's an active read
// request from the application.
if estUntransmittedData > estSenderQuota {
// Sender's window shouldn't go more than 2^31 - 1 as specified in the HTTP spec.
if f.limit+n > maxWindowSize {
f.delta = maxWindowSize - f.limit
} else {
// Send a window update for the whole message and not just the difference between
// estUntransmittedData and estSenderQuota. This will be helpful in case the message
// is padded; We will fallback on the current available window(at least a 1/4th of the limit).
f.delta = n
}
return f.delta
}
return 0
}
// onData is invoked when some data frame is received. It updates pendingData.
func (f *inFlow) onData(n uint32) error {
f.mu.Lock()
f.pendingData += n
if f.pendingData+f.pendingUpdate > f.limit+f.delta {
limit := f.limit
rcvd := f.pendingData + f.pendingUpdate
f.mu.Unlock()
return fmt.Errorf("received %d-bytes data exceeding the limit %d bytes", rcvd, limit)
}
f.mu.Unlock()
return nil
}
// onRead is invoked when the application reads the data. It returns the window size
// to be sent to the peer.
func (f *inFlow) onRead(n uint32) uint32 {
f.mu.Lock()
if f.pendingData == 0 {
f.mu.Unlock()
return 0
}
f.pendingData -= n
if n > f.delta {
n -= f.delta
f.delta = 0
} else {
f.delta -= n
n = 0
}
f.pendingUpdate += n
if f.pendingUpdate >= f.limit/4 {
wu := f.pendingUpdate
f.pendingUpdate = 0
f.mu.Unlock()
return wu
}
f.mu.Unlock()
return 0
}
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