deadlock

README

This program uses a simple "framework" to schedule asynchronous work.

The framework waits for a signal start to cyclically execute a user given handler. Each time it is called, the provided handler may return a result or an error.

The framework supports graceful shutdown: when the process receives a SIGINT, the asynchronous worker is stopped and everything is cleaned up. Before terminating, a goodbye message is written to standard output.

Unfortunately, the graceful shutdown seems not to work. Can you find out why?

Hint

What happen when the signal is received and the asynchronous worker randomize an error?

Solution

When the main goroutine receives the SIGINT signal, it exits from the for - select loop. Then, it signals the background worker to stop using cancel(), before waiting on the WaitGroup at line 111. But if this happens when the worker goroutine is sleeping, when returning from the handler, it will try to send back a result or an error. If it tries to send back an error, it will remain blocked on the channel send, since the errs channel is unbuffered.

Substitute:

errs := make(chan error)

with:

errs := make(chan error, 1)