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// Copyright 2016 Google Inc. All rights reserved.
//
// 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 zip
import (
"fmt"
"runtime"
)
type RateLimit struct {
requests chan request
completions chan int64
stop chan struct{}
}
type request struct {
size int64
serviced chan struct{}
}
// NewRateLimit starts a new rate limiter that permits the usage of up to <capacity> at once,
// except when no capacity is in use, in which case the first caller is always permitted
func NewRateLimit(capacity int64) *RateLimit {
ret := &RateLimit{
requests: make(chan request),
completions: make(chan int64),
stop: make(chan struct{}),
}
go ret.monitorChannels(capacity)
return ret
}
// RequestExecution blocks until another execution of size <size> can be allowed to run.
func (r *RateLimit) Request(size int64) {
request := request{
size: size,
serviced: make(chan struct{}, 1),
}
// wait for the request to be received
r.requests <- request
// wait for the request to be accepted
<-request.serviced
}
// Finish declares the completion of an execution of size <size>
func (r *RateLimit) Finish(size int64) {
r.completions <- size
}
// Stop the background goroutine
func (r *RateLimit) Stop() {
close(r.stop)
}
// monitorChannels processes incoming requests from channels
func (r *RateLimit) monitorChannels(capacity int64) {
var usedCapacity int64
var currentRequest *request
for {
var requests chan request
if currentRequest == nil {
// If we don't already have a queued request, then we should check for a new request
requests = r.requests
}
select {
case newRequest := <-requests:
currentRequest = &newRequest
case amountCompleted := <-r.completions:
usedCapacity -= amountCompleted
if usedCapacity < 0 {
panic(fmt.Sprintf("usedCapacity < 0: %v (decreased by %v)", usedCapacity, amountCompleted))
}
case <-r.stop:
return
}
if currentRequest != nil {
accepted := false
if usedCapacity == 0 {
accepted = true
} else {
if capacity >= usedCapacity+currentRequest.size {
accepted = true
}
}
if accepted {
usedCapacity += currentRequest.size
currentRequest.serviced <- struct{}{}
currentRequest = nil
}
}
}
}
// A CPURateLimiter limits the number of active calls based on CPU requirements
type CPURateLimiter struct {
impl *RateLimit
}
func NewCPURateLimiter(capacity int64) *CPURateLimiter {
if capacity <= 0 {
capacity = int64(runtime.NumCPU())
}
impl := NewRateLimit(capacity)
return &CPURateLimiter{impl: impl}
}
func (e CPURateLimiter) Request() {
e.impl.Request(1)
}
func (e CPURateLimiter) Finish() {
e.impl.Finish(1)
}
func (e CPURateLimiter) Stop() {
e.impl.Stop()
}
// A MemoryRateLimiter limits the number of active calls based on Memory requirements
type MemoryRateLimiter struct {
*RateLimit
}
func NewMemoryRateLimiter(capacity int64) *MemoryRateLimiter {
if capacity <= 0 {
capacity = 512 * 1024 * 1024 // 512MB
}
impl := NewRateLimit(capacity)
return &MemoryRateLimiter{RateLimit: impl}
}
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