async-await-promise.js

/** 
 * Simulate a 1 second computation
 */
function computeFast() {
    console.log("Init fast")
    return new Promise(resolve => {
        setTimeout(function() {
            resolve("  Fast")
            console.log("  End of fast")
        }, 1000)
    })
}

/** 
 * Simulate a 2 seconds computation
 */
function computeSlow() {
    console.log("Init slow")
    return new Promise(resolve => {
        setTimeout(function() {
            resolve("  Slow")
            console.log("  End of slow")
        }, 2000)
    })
}

/**
 * In sequential program, each instruction is executed and completed
 * before the next instruction is executed.
 * Sequential programming is the simplest and most straightforward way of
 * programming, but it does not take advantage of concurrent or parallel execution.
 * It does not involve executing tasks concurrently or in parallel, and therefore
 * it does not make use of multiple computing resources to speed up execution.
 */
async function sequentialStart() {
    console.log('------------------- Sequential -----------------------')
    await computeSlow()
    await computeFast()
}

/**
 * Concurrency refers to the ability of a program to handle multiple tasks
 * concurrently, meaning they can start, execute, and complete in overlapping
 * time intervals. In concurrent programming, tasks are designed to make
 * progress independently, often using techniques such as multitasking,
 * multithreading, or event-driven programming. Concurrency is useful for
 * improving responsiveness and resource utilization, especially in scenarios
 * where tasks involve waiting for external events or input/output operations.
 */
async function concurrentStart() {
    console.log('------------------- Concurrent -----------------------')
    const slow = computeSlow()
    const fast = computeFast()
    await slow
    await fast
    console.log('All concurrent tasks done')
}

/** 
 * Parallelism involves executing multiple tasks simultaneously by utilizing
 * multiple computing resources, such as multiple processors or processor cores.
 * In parallel programming, a program is divided into smaller parts that can be
 * executed simultaneously, with each part assigned to a separate computing resource.
 * Parallelism aims to improve performance and speed up execution by dividing the
 * workload and processing it in parallel.
 */
async function parallel() {
    console.log('------------------- Parallel -----------------------')
    await Promise.all([
        computeSlow(),
        computeFast()
    ]).then(_ => console.log('All parralel tasks done'))
}

sequentialStart()
setTimeout(concurrentStart, 4000)
setTimeout(parallel, 7000)