Golang Standard Library

Dive into golang standard library, where we can learn how high quality code is written and what the golang convention and style is.

sync.WaitGroup⌗

// go version 1.18rc1
type WaitGroup struct {
	noCopy noCopy

	// 64-bit value: high 32 bits are counter, low 32 bits are waiter count.
	// 64-bit atomic operations require 64-bit alignment, but 32-bit
	// compilers only guarantee that 64-bit fields are 32-bit aligned.
	// For this reason on 32 bit architectures we need to check in state()
	// if state1 is aligned or not, and dynamically "swap" the field order if
	// needed.
	state1 uint64
	state2 uint32
}

It’s based on golang semaphore model, implemented by runtime_Semrelease and runtime_Semacquire

semaphore is common mechanism used in concurrent progamming, like Readers–writers problem

Here is an example demostrating how it works, there are three tasks added, one task is done before Wait(), the other two are done after Wait()

• Add() increases or decreases the counter, only reset waiter to 0 when waiter != 0 (which means Wait has already been called then) and release the semaphore.
• Wait() increases the waiter and try to acquire the semaphore.

sync.Pool⌗