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In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available.
On Windows, the Sleep() function takes a single parameter of the number of milliseconds to sleep. The Sleep() function is included in kernel32.dll. [1]The Sleep() function has a resolution no higher than the current timer resolution, typically 16ms but at minimum 1ms, adjustable via the timeBeginPeriod() family of "media timer" APIs.
computes the difference in seconds between two time_t values time: returns the current time of the system as a time_t value, number of seconds, (which is usually time since an epoch, typically the Unix epoch). The value of the epoch is operating system dependent; 1900 and 1970 are often used. See RFC 868. clock
A simple way to understand wait (P) and signal (V) operations is: wait: Decrements the value of the semaphore variable by 1. If the new value of the semaphore variable is negative, the process executing wait is blocked (i.e., added to the semaphore's queue). Otherwise, the process continues execution, having used a unit of the resource.
For this reason, it is usually necessary to enclose each wait operation in a loop like this while not ( P) do wait c where P is some condition stronger than P c. The operations notify c and notify all c are treated as "hints" that P may be true for some waiting thread. Every iteration of such a loop past the first represents a lost notification ...
Wait-freedom is the strongest non-blocking guarantee of progress, combining guaranteed system-wide throughput with starvation-freedom.An algorithm is wait-free if every operation has a bound on the number of steps the algorithm will take before the operation completes. [15]
In computing, a futex (short for "fast userspace mutex") is a kernel system call that programmers can use to implement basic locking, or as a building block for higher-level locking abstractions such as semaphores and POSIX mutexes or condition variables.
This example doesn't use pthread_join() to wait for 2 "newly created" threads to complete. It calls pthread_barrier_wait() inside main(), in order to block the main thread, so that the process will be blocked until 2 threads finish its operation after 5 seconds wait (line 9 - sleep(5)).