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64 lines
1.3 KiB
Go
64 lines
1.3 KiB
Go
// Copyright 2014 Google Inc. All rights reserved.
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// Use of this source code is governed by the Apache 2.0
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// license that can be found in the LICENSE file.
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package internal
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// This file implements a network dialer that limits the number of concurrent connections.
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// It is only used for API calls.
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import (
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"log"
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"net"
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"runtime"
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"sync"
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"time"
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)
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var limitSem = make(chan int, 100) // TODO(dsymonds): Use environment variable.
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func limitRelease() {
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// non-blocking
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select {
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case <-limitSem:
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default:
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// This should not normally happen.
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log.Print("appengine: unbalanced limitSem release!")
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}
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}
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func limitDial(network, addr string) (net.Conn, error) {
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limitSem <- 1
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// Dial with a timeout in case the API host is MIA.
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// The connection should normally be very fast.
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conn, err := net.DialTimeout(network, addr, 500*time.Millisecond)
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if err != nil {
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limitRelease()
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return nil, err
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}
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lc := &limitConn{Conn: conn}
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runtime.SetFinalizer(lc, (*limitConn).Close) // shouldn't usually be required
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return lc, nil
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}
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type limitConn struct {
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mu sync.Mutex // only for closing the net.Conn
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net.Conn
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}
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func (lc *limitConn) Close() error {
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lc.mu.Lock()
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defer lc.mu.Unlock()
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if lc.Conn == nil {
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// Silently ignore double close.
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return nil
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}
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limitRelease()
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err := lc.Conn.Close()
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lc.Conn = nil
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runtime.SetFinalizer(lc, nil)
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return err
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}
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