ossim::Barrier Class Reference

Barrier is a class used to block threads so we can synchronize and entry point. More...

#include <Barrier.h>

Public Member Functions
	Barrier (ossim_int32 n)
	Constructor. More...
	~Barrier ()
	Destructor will reset and release all blocked threads. More...
void	block ()
	block will block the thread based on a wait condition. More...
void	reset ()
	Will reset the barrier to the original values. More...
void	reset (ossim_int32 maxCount)
	Will reset the barrier to a new block count. More...
ossim_int32	getMaxCount () const
ossim_int32	getBlockedCount () const

Protected Attributes
ossim_int32	m_maxCount
ossim_int32	m_blockedCount
std::atomic< ossim_int32 >	m_waitCount
std::mutex	m_mutex
std::condition_variable	m_conditionalBlock
std::condition_variable	m_conditionalWait
	Will be used for destructing and resetting. More...

Detailed Description

Barrier is a class used to block threads so we can synchronize and entry point.

In this example we show how to block the threads so they all start at the same time when executing their work. Example:

#include <ossim/base/Thread.h>
#include <ossim/base/Barrier.h>
int nThreads = 2;
ossim::Barrier barrierStart(nThreads)
// one more for main thread
ossim::Barrier barrierFinished(nThreads+1);

class TestThread : public ossim::Thread
 {
 public:
     TestThread():ossim::Thread(){}
     ~TestThread(){
        waitForCompletion();
     }

  protected:
     virtual void run()
     {
        barrierStart.block();
        for(int x =0 ; x < 10;++x){
           std::cout << "THREAD: " << getCurrentThreadId() << "\n";
           sleepInMilliSeconds(10);
           interrupt();
        }
        barrierFinished.block();
     }
  };

int main(int agrc, char* argv[])
{
   std::vector<std::shared_ptr<TestThread> > threads(nThreads);
   for(auto& thread:threads)
   {
     thread = std::make_shared<TestThread>();
     thread->start();
   }
   // block main until barrier enters their finished state
   barrierFinished.block();

   // you can also reset the barriers and run again
   barrierFinished.reset();
   barrierStart.reset();
   for(auto& thread:threads)
   {
     thread->start();
   }
   barrierFinished.block();
}

Definition at line 69 of file Barrier.h.

Constructor & Destructor Documentation

Barrier()

ossim::Barrier::Barrier

(

ossim_int32

n

)

Constructor.

Parameters

n	is the number of threads you wish to block

Definition at line 3 of file Barrier.cpp.

: m_maxCount(maxCount),
  m_blockedCount(0),
  m_waitCount(0)
{

}

~Barrier()

ossim::Barrier::~Barrier

(

)

Destructor will reset and release all blocked threads.

Definition at line 11 of file Barrier.cpp.

{
   reset();
}

Member Function Documentation

block()

void ossim::Barrier::block

(

)

block will block the thread based on a wait condition.

it will verify if the thread can be blocked by testing if the number of blocked threads is less than the total number to blocked threads. If the total is reached then all threads are notified and woken up and released

Definition at line 16 of file Barrier.cpp.

{
   std::unique_lock<std::mutex> lock(m_mutex);
   ++m_blockedCount;
   if(m_blockedCount < m_maxCount)
   {
      ++m_waitCount;
      m_conditionalBlock.wait(lock, [this]{return m_blockedCount>=m_maxCount;} );
      --m_waitCount;         
   }
   else
   {
      m_conditionalBlock.notify_all();
   }
   // always notify the conditional wait just in case anyone is waiting
   m_conditionalWait.notify_all();
}

getBlockedCount()

ossim_int32 ossim::Barrier::getBlockedCount

(

)

const

Definition at line 66 of file Barrier.cpp.

{
   std::lock_guard<std::mutex> lock(m_mutex);
   return m_blockedCount; 
}

getMaxCount()

ossim_int32 ossim::Barrier::getMaxCount

(

)

const

Definition at line 60 of file Barrier.cpp.

{ 
   std::lock_guard<std::mutex> lock(m_mutex);
   return m_maxCount; 
}

reset() [1/2]

void ossim::Barrier::reset

(

)

Will reset the barrier to the original values.

It will also release all blocked threads and wait for their release before resetting.

Definition at line 34 of file Barrier.cpp.

{
   std::unique_lock<std::mutex> lock(m_mutex);
   // force the condition on any waiting threads
   m_blockedCount = m_maxCount;
   if(m_waitCount.load() > 0){
      m_conditionalBlock.notify_all(); 
      // wait until the wait count goes back to zero
      m_conditionalWait.wait(lock, [this]{return m_waitCount.load()<1;});
   }
   // should be safe to reset everything at this point 
   m_blockedCount = 0;
   m_waitCount    = 0;
}

reset() [2/2]

void ossim::Barrier::reset

(

ossim_int32

maxCount

)

Will reset the barrier to a new block count.

It will also release all blocked threads and wait for their release before resetting.

Parameters

maxCount

is the max number of threads to block

Definition at line 49 of file Barrier.cpp.

{
   // all threads should be released after this call
   reset();
   {
      // now safe to update the new max count
      std::unique_lock<std::mutex> lock(m_mutex);
      m_maxCount = maxCount;
   }
}

Member Data Documentation

m_blockedCount

ossim_int32 ossim::Barrier::m_blockedCount

protected

Definition at line 112 of file Barrier.h.

m_conditionalBlock

std::condition_variable ossim::Barrier::m_conditionalBlock

protected

Definition at line 115 of file Barrier.h.

m_conditionalWait

std::condition_variable ossim::Barrier::m_conditionalWait

protected

Will be used for destructing and resetting.

resetting should only happen in the main thread

Definition at line 122 of file Barrier.h.

m_maxCount

ossim_int32 ossim::Barrier::m_maxCount

protected

Definition at line 111 of file Barrier.h.

m_mutex

std::mutex ossim::Barrier::m_mutex

mutableprotected

Definition at line 114 of file Barrier.h.

m_waitCount

std::atomic<ossim_int32> ossim::Barrier::m_waitCount

protected

Definition at line 113 of file Barrier.h.

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The documentation for this class was generated from the following files:

• Barrier.h
• Barrier.cpp