README.md

Congo - Concurrency Primitives for Go

Package congo includes a CountDownLatch primitive, similar to what's available in the java.util.concurrent package. A CountDownLatch is useful for signaling the completion of the one or more events occurring across multiple goroutines.

Usage

In typical usage, a main goroutine creates the latch with a provided count and passes the latch to a number of goroutines. The goroutines invoke CountDown on the latch to signal completion and reduce the remaining count on the latch. The main goroutine invokes Wait or WaitTimeout on the latch to wait for all events to complete.

For example, the following code:

latch := congo.NewCountDownLatch(3)
for i := 0; i < 3; i++ {
	go func() {
		defer latch.CountDown() // count down after work is complete
		// do work
		// ...
		fmt.Println("Counting down")
	} ()
}
	
	
if (latch.WaitTimeout(5*time.Second)) {
	fmt.Println("Count down complete")
} else {
	fmt.Println("Count down not complete")
}

Produces output:

Counting down
Counting down
Counting down
Count down complete

CountDownLatch vs. sync.WaitGroup

CountDownLatch is similar to WaitGroup in the standard Go sync package with a few notable differences:

• Caller can wait with a timeout (WaitTimeout) for the count down to complete.
• Caller can retrieve the current count using Count to track the progress of latch count down completion.
• Couple of extra ways to CountDown:
  • WeightedCountDown reduces the remaining count by a specified number.
  • Complete reduces the remaining count to 0 and signals any waiting goroutines immediately.
• The starting count is set once at the time of creating the CountDownLatch. This avoids the potential for misuse of the WaitGroup.Add function, which should only be invoked in the main goroutine.

Installation

To install congo, use go get:

go get github.com/nvn1729/congo

Then import the github.com/nvn1729/congo into your code:

import "github.com/nvn1729/congo"

Documentation

Blog Post