Second worker thread should start after first has finished it task.

[learningvisualc]

Hi all, I have two worker thread. one thread is populating the list and second thread is doing operation on that list. my problem is i want that after i have populated the list then only second thread should start. How can i do it? Thanks in advance

[KingsGambit]

In the second thread you can use WaitForSingleObject() to wait for the first thread's handle to complete.

[Eytukan]

1. Start 1st thread. 2. Wait for it to finish. 3. Start 2nd thread.

learningvisualc wrote:

my problem is

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Starting to think people post kid pics in their profiles because that was the last time they were cute - Jeremy.

[Cedric Moonen]

In addition to the previous answer: is there a particular reason why you want to use a second thread ? You have to wait until the first thread is finished, so why don't you simply execute that task in the same thread as the first one. I don't really see an added value of starting a second thread when the first one terminates.

Cédric Moonen Software developer
Charting control [v3.0] OpenGL game tutorial in C++

[Xie Jinghui]

//
#include "stdafx.h"

#include "iostream"
using namespace std;

HANDLE hThread1 = NULL; //worker thread 1
HANDLE hThread2 = NULL; //worker therad 2

HANDLE hEvt1 = NULL;

DWORD __stdcall ThreadProc_1( LPVOID lpParameter )
{
// populating the list ...
for(int i = 0; i<10; i++)
{
cout<<"populating the list -- "<<i<<endl;
}

// after populate the list , set event, then the worker thread 2 will stop waiting and do operation on the list...
::SetEvent(hEvt1);

return 0;

}

DWORD __stdcall ThreadProc_2( LPVOID lpParameter )
{
// wait
while(::WaitForSingleObject(hEvt1, 5) == WAIT_TIMEOUT)
{
//keep waiting ...
Sleep(5);
continue;
}

// To do operation on that list...
for(int i = 0; i<10; i++)
{
	cout<<"doing operation on that list -- "<<i<<endl;
}

return 0;

}

int _tmain(int argc, _TCHAR* argv[])
{
hEvt1 = CreateEvent(NULL, TRUE, FALSE, NULL);

//Create the two worker threads
hThread1 = CreateThread(NULL, 0, ThreadProc\_1, NULL, 0, NULL);
hThread2 = CreateThread(NULL, 0, ThreadProc\_2, NULL, 0, NULL);

// waiting , 
while(::WaitForSingleObject(hThread2, 5) == WAIT\_TIMEOUT)
{
	Sleep(5);
	continue;
}

if(hThread1)
	::CloseHandle(hThread1);
if(hThread2)
	::CloseHandle(hThread2);

if(hEvt1)
	::CloseHandle(hEvt1);

return 0;

}

[Xie Jinghui]

quite right

[Sauro Viti]

1. Xie Jinghui wrote:

   while(::WaitForSingleObject(hEvt1, 5) == WAIT_TIMEOUT)
   {
   //keep waiting ...
   Sleep(5);
   continue;
   }

   This has the same effect than:

   ::WaitForSingleObject(hEvt1, INFINITE);

   but is more complex and less efficient as the OS every 5 seconds schedule the thread to be runt again; using a wait timeout of INFINITE is better because the OS suspend the thread and resume it only when the eventis signeled.

2. You don't really need to create an event: the second thread could simply wait for the first thread to terminate

   ::WaitForSingleObject(hThread1, INFINITE);

[Xie Jinghui]

Thank you, :) I always overlook the details,,, the program will be more efficient,

[Aescleal]

Make it single threaded - threads are only useful when doing parallel operatations, they're only overhead otherwise. Cheers, Ash