Why Do Go Applications Hang When Using WaitGroups and Channels?

Closing Channels for Clean Exit in Go Applications Using WaitGroups

This article investigates a common issue faced when using sync.WaitGroup and channels in Go programs, which can prevent the main function from exiting after all goroutines have completed their tasks. Let's explore the problem and its solution.

The Problem: Infinite Wait

In the provided example, the main function utilizes a sync.WaitGroup and a channel (fetchedSymbols) to manage concurrent goroutines that fetch and save stock quotes. While the goroutines do complete their tasks, the program hangs indefinitely without exiting.

The Issue: Non-Closed Channel

The culprit is the range loop in the main function. Iterating over the fetchedSymbols channel blocks the progress because the channel is never closed. As a result, the main function waits indefinitely for new values to be sent through the channel, even though all values have already been received.

The Solution: Closing the Channel

To resolve this issue, it's crucial to close the fetchedSymbols channel once all goroutines have completed their tasks. This signals to the range loop that there are no more values to receive, allowing the iteration to end and the main function to proceed.

One approach is to use the Wait method of the sync.WaitGroup to signal when all goroutines have finished. A goroutine can be launched to wait for the WaitGroup to reach zero and then close the channel.

<code class="go">go func() {
    wg.Wait()
    close(fetchedSymbols)
}()</code>

With this modification, the range loop in the main function will eventually reach the end of the channel, allowing the program to print the "done" message and exit gracefully.

By understanding the importance of closing channels when working with sync.WaitGroup, Go developers can ensure that their applications terminate predictably after executing concurrent tasks.

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