Software

Software-defined mutual exclusion implementations are all based on busy-waiting. An example is Dekker's algorithm, which defines a system in which two processes can synchronize, employing busy-wait to wait for the other process to leave the critical section.

The pseudocode for this algorithm is as follows:

    variables
        wants_to_enter : array of 2 booleans
        turn : integer

    wants_to_enter[0] ← false
    wants_to_enter[1] ← false
    turn ← 0 // or 1

p0:
    wants_to_enter[0] ← true
    while wants_to_enter[1] {
        if turn ≠ 0 {
            wants_to_enter[0] ← false
            while turn ≠ 0 {
                // busy wait
            }
            wants_to_enter[0] ← true
        }
    }
    // critical section
    ...
    turn ← 1
    wants_to_enter[0] ← false
    // remainder section

p1:
    wants_to_enter[1] ← true
    while wants_to_enter[0] {
        if turn ≠ 1 {
            wants_to_enter[1] ← false
            while turn ≠ 1 {
                // busy wait
            }
            wants_to_enter[1] ← true
        }
    }
    // critical section
    ...
    turn ← 0
    wants_to_enter[1] ← false
    // remainder section

(Referenced from: )