100 lines
2.9 KiB
Go
100 lines
2.9 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package cmd
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import (
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"errors"
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"net/http"
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"sync"
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)
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var errTooManyRequests = errors.New("Too many clients in the waiting list")
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// rateLimit - represents datatype of the functionality implemented to
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// limit the number of concurrent http requests.
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type rateLimit struct {
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handler http.Handler
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lock sync.Mutex
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workQueue chan struct{}
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waitQueue chan struct{}
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}
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// acquire and release implement a way to send and receive from the
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// channel this is in-turn used to rate limit incoming connections in
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// ServeHTTP() http.Handler method.
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func (c *rateLimit) acquire() error {
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//lock access to enter waitQueue
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c.lock.Lock()
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// Kick out clients when it is really crowded
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if len(c.waitQueue) == cap(c.waitQueue) {
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defer c.lock.Unlock() //unlock after return
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return errTooManyRequests
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}
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// Add new element in waitQueue to keep track of clients
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// wanting to process their requests
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c.waitQueue <- struct{}{}
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// Unlock now. If we unlock before sending to the waitQueue
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// channel, we can have multiple go-routines blocked on
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// sending to the waitQueue (and exceeding the max. number of
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// waiting connections.)
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c.lock.Unlock()
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// Block to put a waiting go-routine into processing mode.
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c.workQueue <- <-c.waitQueue
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return nil
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}
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// Release one element from workQueue to serve a new client
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// in the waiting list
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func (c *rateLimit) release() {
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<-c.workQueue
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}
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// ServeHTTP is an http.Handler ServeHTTP method, implemented to rate
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// limit incoming HTTP requests.
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func (c *rateLimit) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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// Acquire the connection if queue is not full, otherwise
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// code path waits here until the previous case is true.
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if err := c.acquire(); err != nil {
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w.WriteHeader(http.StatusTooManyRequests)
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return
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}
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// Serves the request.
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c.handler.ServeHTTP(w, r)
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// Release
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c.release()
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}
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// setRateLimitHandler limits the number of concurrent http requests based on MINIO_MAXCONN.
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func setRateLimitHandler(handler http.Handler) http.Handler {
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if globalMaxConn == 0 {
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return handler
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} // else proceed to rate limiting.
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// For max connection limit of > '0' we initialize rate limit handler.
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return &rateLimit{
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handler: handler,
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workQueue: make(chan struct{}, globalMaxConn),
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waitQueue: make(chan struct{}, globalMaxConn*4),
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}
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}
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