Mailbox.h

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/*
   For more information, please see: http://software.sci.utah.edu

   The MIT License

   Copyright (c) 2009 Scientific Computing and Imaging Institute,
   University of Utah.

   
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///
///@file   Mailbox.h
///@brief  Threadsafe FIFO
///
///@author Steve Parker
///        Department of Computer Science
///        University of Utah
///@date   June 1997
///

#ifndef Core_Thread_Mailbox_h
#define Core_Thread_Mailbox_h

#include <Core/Thread/Legacy/Legacy/ConditionVariable.h>
#include <Core/Thread/Legacy/Legacy/Mutex.h>
#include <Core/Thread/Legacy/Legacy/Semaphore.h>
#include <Core/Thread/Legacy/Legacy/Thread.h>

#include <vector>


namespace SCIRun {
/**************************************

@class
  Mailbox

  KEYWORDS
  Thread, FIFO

@details
  A thread-safe, fixed-length FIFO queue which allows multiple
  concurrent senders and receivers.  Multiple threads send <b>Item</b>s
  to the mailbox, and multiple thread may receive <b>Item</b>s from the
  mailbox.  Items are typically pointers to a message structure.

****************************************/
template<class Item> class Mailbox {
public:
  //////////
  /// Create a mailbox with a maximum queue size of <i>size</i>
  /// items. If size is zero, then the mailbox will use
  /// <i>rendevous semantics</i>, where a sender will block
  /// until a reciever is waiting for the item.  The item will
  /// be handed off synchronously. <i>name</i> should be a
  /// static string which describes the primitive for debugging
  /// purposes.
  Mailbox(const char* name, int size);
    
  //////////
  /// Destroy the mailbox.  All items in the queue are silently
  /// dropped.
  ~Mailbox();
    
  //////////
  /// Puts <i>msg</i> in the queue.  If the queue is full, the
  /// thread will be blocked until there is room in the queue.
  /// Messages from the same thread will be placed in the
  /// queue in a first-in/first out order. Multiple threads may
  /// call <i>send</i> concurrently, and the messages will be
  /// placed in the queue in an arbitrary order.
  void send(const Item& msg);
    
  //////////
  /// Attempt to send <i>msg</i> to the queue.  If the queue is
  /// full, the thread will not be blocked, and <i>trySend</i>
  /// will return false.  Otherwise, <i>trySend</i> will return
  /// true.  This may never complete if the reciever only uses
  /// <i>tryRecieve</i>.  
  bool trySend(const Item& msg);
    
  
  //////////
  /// Send <i>msg</i> to the queue only if the <i>checker</i> function
  /// fails to compare the <i>msg</i> to what is already the last item
  /// there.  This is useful if we want to make certain that at least
  /// one of a particular message (like a viewer resize redraw) gets
  /// put on the mailbox without spamming it.  This blocks like
  /// <i>send</i> does.  It returns true if <i>msg</i> was added to the
  /// queue and false if it wasn't.
  bool sendIfNotSentLast(const Item& msg,
                         bool (*checker)(const Item &a, const Item &b));

  //////////
  /// Receive an item from the queue.  If the queue is empty,
  /// the thread will block until another thread sends an item.
  /// Multiple threads may call <i>recieve</i> concurrently, but
  /// no guarantee is made as to which thread will recieve the
  /// next token.  However, implementors should give preference
  /// to the thread that has been waiting the longest.
  Item receive();

  //////////
  /// Attempt to recieve <i>item</i> from the mailbox.  If the
  /// queue is empty, the thread is blocked and <i>tryRecieve</i>
  /// will return false.  Otherwise, <i>tryRecieve</i> returns true.
  bool tryReceive(Item& item);
    
  //////////
  /// Return the maximum size of the mailbox queue, as given in the
  /// constructor.
  int size() const;

  //////////
  /// Return the number of items currently in the queue.
  int numItems() const;

private:
  const char* name_;
  Mutex mutex_;
  std::vector<Item> ring_buffer_;
  int head_;
  int len_;
  int max_;
  ConditionVariable empty_;
  ConditionVariable full_;
  Semaphore rendezvous_;
  int send_wait_;
  int recv_wait_;
  inline int ringNext(int inc);

  // Cannot copy them
  Mailbox(const Mailbox<Item>&);
  Mailbox<Item> operator=(const Mailbox<Item>&);
};

template<class Item> inline
int
Mailbox<Item>::ringNext(int inc)
{
    return max_==0?0:((head_+inc)%max_);
}

template<class Item>
Mailbox<Item>::Mailbox(const char* name, int size)
    : name_(name), mutex_("Mailbox lock"), ring_buffer_(size==0?1:size),
      empty_("Mailbox empty condition"), full_("Mailbox full condition"),
      rendezvous_("Mailbox rendezvous semaphore", 0)
{
    head_=0;
    len_=0;
    send_wait_=0;
    recv_wait_=0;
    max_=size;
}

template<class Item>
Mailbox<Item>::~Mailbox()
{
  mutex_.tryLock();
  mutex_.unlock();

  // release all waiting threads
  //  empty_.conditionBroadcast();
  //  full_.conditionBroadcast();
}

template<class Item>
void
Mailbox<Item>::send(const Item& msg)
{
    int s=Thread::couldBlock(name_);
    mutex_.lock();
    // See if the message buffer is full...
    int rmax=max_==0?1:max_;
    while(len_ == rmax){
        send_wait_++;
        full_.wait(mutex_);
        send_wait_--;
    }
    ring_buffer_[ringNext(len_)]=msg;
    len_++;
    if(recv_wait_)
        empty_.conditionSignal();
    mutex_.unlock();
    if(max_==0)
        rendezvous_.down();
    Thread::couldBlockDone(s);
}

template<class Item>
bool
Mailbox<Item>::trySend(const Item& msg)
{
    mutex_.lock();
    // See if the message buffer is full...
    int rmax=max_==0?1:max_;
    if(len_ == rmax){
        mutex_.unlock();
        return false;
    }
    if(max_ == 0 && recv_wait_==0){
        // No receivers waiting, so rendezvous will fail. Return now.
        mutex_.unlock();
        return false;
    }

    ring_buffer_[ringNext(len_)]=msg;
    len_++;
    if(recv_wait_)
        empty_.conditionSignal();
    mutex_.unlock();
    if(max_==0)
        rendezvous_.down();  // Won't block for long, since a receiver
                            // will wake us up
    return true;
}


template<class Item>
bool
Mailbox<Item>::sendIfNotSentLast(const Item& msg,
                                 bool (*checker)(const Item &a, const Item &b))
{
    int s = Thread::couldBlock(name_);
    mutex_.lock();
    // See if the message buffer is full...
    int rmax=max_==0?1:max_;
    while(len_ == rmax){
        send_wait_++;
        full_.wait(mutex_);
        send_wait_--;
    }
    if (len_ < 1 || checker(ring_buffer_[ringNext(len_-1)], msg))
    {
      ring_buffer_[ringNext(len_)]=msg;
      len_++;
      if(recv_wait_)
        empty_.conditionSignal();
      mutex_.unlock();
      if(max_==0)
        rendezvous_.down();
      Thread::couldBlockDone(s);
      return true;
    }
    else
    {
      mutex_.unlock();
      Thread::couldBlockDone(s);
      return false;
    }
}


template<class Item>
Item
Mailbox<Item>::receive()
{
    int s=Thread::couldBlock(name_);
    mutex_.lock();
    while(len_ == 0){
        recv_wait_++;
        empty_.wait(mutex_);
        recv_wait_--;
    }
    Item val=ring_buffer_[head_];
    ring_buffer_[head_] = 0; //if it is a handle clear it.
    head_=ringNext(1);
    len_--;
    if(send_wait_)
        full_.conditionSignal();
    mutex_.unlock();
    if(max_==0)
        rendezvous_.up();
    Thread::couldBlockDone(s);
    return val;
}

template<class Item>
bool
Mailbox<Item>::tryReceive(Item& item)
{
    mutex_.lock();
    if(len_ == 0){
        mutex_.unlock();
        return false;
    }
    item=ring_buffer_[head_];
    ring_buffer_[head_] = 0; //if it is a handle clear it.
    head_=ringNext(1);
    len_--;
    if(send_wait_)
        full_.conditionSignal();
    mutex_.unlock();
    if(max_==0)
        rendezvous_.up();
    return true;
}

template<class Item>
int
Mailbox<Item>::size() const
{
    return max_;
} // End namespace SCIRun

template<class Item>
int
Mailbox<Item>::numItems() const
{
    return len_;
}

} // End namespace SCIRun
#endif