If the returnfloat parameter is set to TRUE, it returns a float representing the current time in seconds since the Unix epoch accurate to. This is different than running a standard 1 second sleep loop, due to sleeping longer does not consume as much CPU. The difference between sleep() and usleep() is that sleep() takes a number of seconds as its parameter, whereas usleep() takes a number of microseconds -. Return Value: Returns the string 'microsec sec' by default, where sec is the number of seconds since the Unix Epoch (0:00:00 JanuGMT), and microsec is the microseconds part.

This is not a replacement for multi-threading, but it could help someone that wants to do something cheap. so if you have to wait for something, go to sleep for a few seconds instead of occupying the cpu while doing absolute nothing but waitting. what results in better response times and lower overall system-load.

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Php sleep millisec