Why Does Sending Two Values to a Channel Cause a Deadlock in This Go Code?

Go Channels and Deadlocks

The provided Go code snippet illustrates a classic deadlock issue involving channels. When only one value is sent to channel c1, the code operates as intended, exchanging values back and forth between goroutines via channels c1 and c2. However, sending a second value to c1 from the main goroutine leads to a deadlock.

The deadlock occurs because the two goroutines are continuously sending values between the channels without a mechanism for consuming or exiting the loop. Each goroutine waits for a value on its respective channel, and when one arrives, it sends it back to the other channel. This creates an infinite loop where neither goroutine can progress.

Debugging Deadlocks

There are several techniques for debugging deadlocks in Go code:

• Kill Signal: Sending a kill signal (e.g., kill -6 [pid] on Unix-like systems) to the running process will terminate it and print a stack trace for each goroutine. This can help identify the location of the deadlock.
• GDB Debugging: Attaching gdb to the running process (gdb [executable name] [pid]) allows you to inspect the stack and variables of the active goroutine. However, switching between goroutines is not straightforward.
• Channel Buffering: Using buffered channels with a size greater than zero can prevent deadlocks by allowing values to be sent and received without blocking. However, it is essential to consider the implications of using buffered channels and ensure they align with the intended behavior of the code.

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