Cyclic data reading (like 1Wire DS18B20 temperature) without blocking main program - c

Question

I'm trying to do some temperature reading using DS18B20 sensor on Raspberry Pi. My problem is that reading data from this sensor takes time. It's not much, more or less 1 s, but I cannot allow my main program to wait until this is done. I don't need to have 'most recent value'. It's temperature, so I'm gonna ask about it every minute or so. But the sensor can make measurement for example every 10 s and this will provide me recent enough value. In mean time I have to process other requests made to application. So I am thinking of some kind of endless measure loop. In general it would look like:
> start time measurement
> get DS18B20 value from 1 wire
> parse output
> stop measure time
> get the execution time, and put it in some global variable
> sleep for UPDATE_EVERY_X - execution time
So I thought of using fork(), but this creates zombies when the main process exit. Main application is some kind of server, so it won't exit gently in most times, so I need some kind of additional protection and this should be not Linux unique method. I'm trying to write my app as portable I can.
Second thought of mine is to use threads. Dispatch one thread to do this infinite loop, and implement some basic producer - consumer, with mutexes etc. That thread will only lock the output temperature when all is done, so this will make significant difference in blocking time.
Third option is to use asynchronous IO. But this is kind of magic for me right know. I did not used this before but it appears in search results.
And for claryfication, this is not strictly about 1Wire DS18B20, but about main approach when you need to do task every x sec and share information between processes, kind of embedded timer interupts.
Best regards, voodoo16.

Answer 1

If you want the simplest option, remember that the "Convert T" and "Read Scratchpad" commands are two distinct steps. Your program can read the temperature, then come back for the value later. There's no need to stall the program, unless you want to get the temperature value the exact instant the conversion finishes.
mainLoop() {
while(1) {
// Do things
int16_t rawTemperature = readScratchpad(myTemperatureSensor); // Get the last temperature reading
if(!getTemperature(myTemperatureSensor)) { // Start the next conversion
//Temperature conversion was not done, throw out value
rawTemperature = INT16_MAX;
}
else {
float temperature = ((float)rawTemperature / 4.0f);
saveTemperature(temperature);
}
// Do other things while temperature conversion happens
}
}
Where in this case, getTemperature issues a "Convert T" command, and returns 0 or 1 according to the datasheet (replies 0 if the prior conversion wasn't done, 1 if a new conversion has been started).