ACE 领导者-跟随者线程池 选举方案

ACE 领导者-跟随者线程池 选举方案

分析 ACE LF_ThreadPool 例子中的 领导者选举方案，增加一种新的选举方案，见源代码分析。

ACE例子源代码如下：

// $Id: LF_ThreadPool.cpp 94310 2011-07-09 19:10:06Z schmidt $#include "ace/config-lite.h"#if defined (ACE_HAS_THREADS)#include "ace/OS_NS_string.h"#include "ace/OS_NS_sys_time.h"#include "ace/Task.h"#include "ace/Containers.h"#include "ace/Synch.h"#include "ace/Condition_T.h"// Listing 4 code/ch16class Follower{public:  Follower (ACE_Thread_Mutex &leader_lock)    : cond_(leader_lock)  {    owner_ = ACE_Thread::self ();  }  //FUZZ: disable check_for_lack_ACE_OS  int wait (void)  {    return this->cond_.wait ();  }  int signal (void)  {    return this->cond_.signal ();  }  //FUZZ: enable check_for_lack_ACE_OS  ACE_thread_t owner (void)  {    return this->owner_;  }private:  ACE_Condition<ACE_Thread_Mutex> cond_;  ACE_thread_t owner_;};// Listing 4// Listing 1 code/ch16class LF_ThreadPool : public ACE_Task<ACE_MT_SYNCH>{public:  LF_ThreadPool () : shutdown_(0), current_leader_(0)  {    ACE_TRACE ("LF_ThreadPool::TP");  }  virtual int svc (void);  void shut_down (void)  {    shutdown_ = 1;  }private:  int become_leader (void);  Follower *make_follower (void);  int elect_new_leader (void);  int leader_active (void)  {    ACE_TRACE ("LF_ThreadPool::leader_active");    return this->current_leader_ != 0;  }  void leader_active (ACE_thread_t leader)  {    ACE_TRACE ("LF_ThreadPool::leader_active");    this->current_leader_ = leader;  }  void process_message (ACE_Message_Block *mb);  int done (void)  {    return (shutdown_ == 1);  }private:  int shutdown_;  ACE_thread_t current_leader_;  ACE_Thread_Mutex leader_lock_;  ACE_Unbounded_Queue<Follower*> followers_;  ACE_Thread_Mutex followers_lock_;  static long LONG_TIME;};// Listing 1// Listing 2 code/ch16intLF_ThreadPool::svc (void){  ACE_TRACE ("LF_ThreadPool::svc");  while (!done ())    {      //elect_new_leader ();//这种选举方案，当没有消息时，池内线程轮流坐庄  add by zhangjiancheng      become_leader ();  // Block until this thread is the leader.      ACE_Message_Block *mb = 0;      ACE_Time_Value tv (LONG_TIME);      tv += ACE_OS::gettimeofday ();      // Get a message, elect new leader, then process message.      if (this->getq (mb, &tv) < 0)        {          if (elect_new_leader () == 0)            break;          continue;        }  elect_new_leader (); //这种选举方案，当没有消息时，当前领导者阻塞，直至新消息到达，再重新选举领导者 note by zhangjiancheng

      process_message (mb);    }  return 0;}// Listing 2// Listing 3 code/ch16intLF_ThreadPool::become_leader (void){  ACE_TRACE ("LF_ThreadPool::become_leader");  ACE_GUARD_RETURN    (ACE_Thread_Mutex, leader_mon, this->leader_lock_, -1);  if (leader_active ())    {      Follower *fw = make_follower ();      {        // Wait until told to do so.        while (leader_active ())          fw->wait ();      }      delete fw;    }  ACE_DEBUG ((LM_DEBUG, ACE_TEXT ("(%t) Becoming the leader\n")));  // Mark yourself as the active leader.  leader_active (ACE_Thread::self ());  return 0;}Follower*LF_ThreadPool::make_follower (void){  ACE_TRACE ("LF_ThreadPool::make_follower");  ACE_GUARD_RETURN    (ACE_Thread_Mutex, follower_mon, this->followers_lock_, 0);  Follower *fw;  ACE_NEW_RETURN (fw, Follower (this->leader_lock_), 0);  this->followers_.enqueue_tail (fw);  return fw;}// Listing 3// Listing 5 code/ch16intLF_ThreadPool::elect_new_leader (void){  ACE_TRACE ("LF_ThreadPool::elect_new_leader");  ACE_GUARD_RETURN    (ACE_Thread_Mutex, leader_mon, this->leader_lock_, -1);  leader_active (0);  // Wake up a follower  if (!followers_.is_empty ())    {      ACE_GUARD_RETURN (ACE_Thread_Mutex,                        follower_mon,                        this->followers_lock_,                        -1);      // Get the old follower.      Follower *fw;      if (this->followers_.dequeue_head (fw) != 0)        return -1;  //leader_active (fw->owner());      ACE_DEBUG ((LM_DEBUG,                  ACE_TEXT ("(%t) Resigning and Electing %d\n"),                  fw->owner ()));      return (fw->signal () == 0) ? 0 : -1;    }  else    {      ACE_DEBUG        ((LM_ERROR, ACE_TEXT ("(%t) Oops no followers left\n")));      return -1;    }}// Listing 5voidLF_ThreadPool::process_message (ACE_Message_Block *mb){  ACE_TRACE ("LF_ThreadPool::process_message");  int msgId;  ACE_OS::memcpy (&msgId, mb->rd_ptr (), sizeof(int));  mb->release ();  ACE_DEBUG ((LM_DEBUG,              ACE_TEXT ("(%t) Started processing message:%d\n"),              msgId));  ACE_OS::sleep (1);  ACE_DEBUG ((LM_DEBUG,              ACE_TEXT ("(%t) Finished processing message:%d\n"),              msgId));}long LF_ThreadPool::LONG_TIME = 5L;int ACE_TMAIN (int, ACE_TCHAR *[]){  LF_ThreadPool tp;  tp.activate (THR_NEW_LWP| THR_JOINABLE, 5);  // Wait for a few seconds...  ACE_OS::sleep (2);  ACE_Time_Value tv (1L);  ACE_Message_Block *mb = 0;  for (int i = 0; i < 30; i++)    {      ACE_NEW_RETURN (mb, ACE_Message_Block (sizeof(int)), -1);      ACE_OS::memcpy (mb->wr_ptr (), &i, sizeof(int));      ACE_OS::sleep (tv);      // Add a new work item.      tp.putq (mb);    }  ACE_Thread_Manager::instance ()->wait ();  ACE_OS::sleep (10);  return 0;}#else#include "ace/OS_main.h"#include "ace/OS_NS_stdio.h"int ACE_TMAIN (int, ACE_TCHAR *[]){  ACE_OS::puts (ACE_TEXT ("This example requires threads."));  return 0;}#endif /* ACE_HAS_THREADS */