src/comm/AcceptLimiter.h

   1 /*
   2  * Copyright (C) 1996-2014 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef _SQUID_SRC_COMM_ACCEPT_LIMITER_H
  10 #define _SQUID_SRC_COMM_ACCEPT_LIMITER_H
  11
  12 #include "comm/TcpAcceptor.h"
  13
  14 #include <vector>
  15
  16 namespace Comm
  17 {
  18
  19 /**
  20  * FIFO Queue holding listener socket handlers which have been activated
  21  * ready to dupe their FD and accept() a new client connection.
  22  * But when doing so there were not enough FD available to handle the
  23  * new connection. These handlers are awaiting some FD to become free.
  24  *
  25  * defer - used only by Comm layer ConnAcceptor adding themselves when FD are limited.
  26  * removeDead - used only by Comm layer ConnAcceptor to remove themselves when dying.
  27  * kick - used by Comm layer when FD are closed.
  28  */
  29 /* TODO this algorithm can be optimized further:
  30  *
  31  * 1) reduce overheads by only pushing one entry per port to the list?
  32  * use TcpAcceptor::isLimited as a flag whether to re-list when kick()'ing
  33  * or to NULL an entry while scanning the list for empty spaces.
  34  * Side effect: TcpAcceptor->kick() becomes allowed to pull off multiple accept()'s in bunches
  35  *
  36  * 2) re-implement as a std::queue instead of std::vector
  37  * storing head/tail pointers for fast push/pop and avoiding the whole shift() overhead
  38  */
  39 class AcceptLimiter
  40 {
  41
  42 public:
  43     /** retrieve the global instance of the queue. */
  44     static AcceptLimiter &Instance();
  45
  46     /** delay accepting a new client connection. */
  47     void defer(const TcpAcceptor::Pointer &afd);
  48
  49     /** remove all records of an acceptor. Only to be called by the ConnAcceptor::swanSong() */
  50     void removeDead(const TcpAcceptor::Pointer &afd);
  51
  52     /** try to accept and begin processing any delayed client connections. */
  53     void kick();
  54
  55 private:
  56     static AcceptLimiter Instance_;
  57
  58     /** FIFO queue */
  59     std::vector<TcpAcceptor::Pointer> deferred_;
  60 };
  61
  62 }; // namepace Comm
  63
  64 #endif /* _SQUID_SRC_COMM_ACCEPT_LIMITER_H */
  65