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Create a block / wait function?

Posted on 2004-08-17
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Last Modified: 2011-04-14
I am looking for a way to create a function that, like the sockets accept function,
blocks / waits untill a specific variable is set or a specific function is called.
At the moment I am using the very system expensive code:
while(!input);

I need a function that can be called inside a thread procedure to keep the thread from consuming all of the processors power.

Any ideas?



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Question by:chrille_p
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7 Comments
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 11819148
On Windows platform use

    Sleep(1);    // wait 1 millisecond

in your loop.

Regards, Alex
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LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 11819159
OS/2 you have to use DosSleep, and *NIX it is sleep (as far as i remember).

Regards, Alex
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LVL 39

Accepted Solution

by:
itsmeandnobodyelse earned 1000 total points
ID: 11819214
On Windows platform you also may wait on an event rather than on some time elapsed. You may either use WaitForSingleObject or WaitForMultipleObjects:

MSDN says:

The WaitForSingleObject function can wait for the following objects:

Change notification
Console input
Event
Job
Mutex
Process
Semaphore
Thread
Waitable timer

Regards, Alex

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Author Comment

by:chrille_p
ID: 11819311
Im not looking for a function that waits for a couple of seconds.
What I want is a thread-procedure (A) that waits untill function (B) is called...

I could use sleep() in my loop and check a flag every n second, but that would make
the reaction of my function slow. I want it to stop waiting and continue its work
directly when (B) is called.

/Chrille
0
 

Author Comment

by:chrille_p
ID: 11819344
WaitForSingleObject is perfect.

Thanks!

/Chrille
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LVL 22

Expert Comment

by:grg99
ID: 11819346
Depending on the OS, there may be a Sleep() function that is calibrated in milliseconds.

Otherwise you could find some API, any API, that will do a task-switch for you.
On Windows that puts your thread to sleep for about 20-30 milliseconds, a nice ballpark sleep time.

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LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 11819381
>> Im not looking for a function that waits for a couple of seconds.

Ok, but before using
 
    while(!input);

you should have

    while(!input) { sleep(1); }


>> What I want is a thread-procedure (A) that waits untill function (B) is called...

You could use a mutex that gets locked by your main thread, then your thread is waiting on the mutex to be unlocked, what is done at the beginning of function B .

What OS are you working on?

Regards, Alex




 

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