Why do Unbuffered Channels in Go Lead to Deadlock?

Go Channels and Deadlock

Understanding the issue

The code provided demonstrates two goroutines communicating through channels. While one channel successfully sends and receives data between the goroutines, deadlocks occur when an additional value is sent to one of the channels from the main function.

Explanation

This deadlock is due to the absence of any buffering in the channels. Since the channels are unbuffered, each goroutine must be ready to send and receive data simultaneously. When the main function sends the second value to c1, the first goroutine is waiting to receive from c2. Simultaneously, the second goroutine is waiting to send to c1. Therefore, both goroutines are waiting for the other to proceed, resulting in a deadlock.

Debugging techniques

To debug such deadlocks, several techniques can be employed:

• Using kill -6 on Unix systems: This command kills the program and dumps the stack trace of each goroutine.
• Attaching gdb: Attaching a debugger like gdb allows you to examine the stack and variables of the active goroutine, but switching between goroutines may not be straightforward.

Mitigation

To avoid deadlocks with unbuffered channels, consider adding a buffer to at least one of the channels. This allows one goroutine to advance ahead of the other, preventing a deadlock situation. Alternatively, use synchronized access to the channels to ensure that only a single goroutine can send or receive data at a time.

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