how to schedule a c function to run exactly every minute

Question

I have a thread that i have created using pthread should be run exactly every minute . How can I do this in c program to run it every minute.sleep doent solve my problem .

Answer 1

I'm assuming^(a) you mean sleep is no good because if you sleep for 60 seconds following a seven-second job, that won't be every minute.

So, in order to go every minute regardless of how long the job takes, you can use something like (pseudo-code):

def threadFn():
    lastTime = now()  # or now() - 60 to run first one immediately.
    do forever:
        currTime = now()
        if currTime - lastTime >= 60:
            lastTime = currTime
            doPayload()
        sleep one second

This of course has the shortcoming that, if your job takes more than a minute, the next iteration of it will be delayed. But, short of having to handle multiple concurrent jobs, that's probably best.

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^(a) That seems the most likely possibility to me but it's an assumption I probably needn't have made if you'd included the code and/or added detail as to why it was a problem :-)

As another possibility, to ensure it only runs at hh:mm:00 (i.e., exactly on the minute switch-over), you could do a slight variation:

def threadFn():
    lastTime = now() - 1 # Ensure run at first hh:mm:00.
    do forever:
        currTime = now()
        currSec = getSecond(currTime) # using C's localtime()
        if currSec == 0 and currTime != lastTime:
            lastTime = currTime
            doPayload()
        sleep one tenth of a second

The reduced sleep is to ensure you run the payload as quickly as possible after entering the new minute.