Go Runtime: Mystery of the Infinite Loop in Main Function

In the heart of Go's runtime lies src/runtime/proc.go, where a puzzling feature resides: an infinite for loop at the tail end of the main function. One might wonder why such a seemingly pointless construct exists in the runtime.

Purpose: Detecting Fatal Errors

Delving into the code, it becomes clear that the loop serves a crucial purpose in error handling. When panic is called with a fatal error, it executes a chain of operations, culminating in a call to exit(0). However, under certain circumstances, exit can fail, leaving the program in limbo.

Enter the Endless Loop

In such cases, Go employs a fallback mechanism: the infinite for loop. By assigning 0 to a protected memory region (*x = 0), it provokes a segmentation fault. This causes the program to crash gracefully, preventing unexpected behavior.

Design Considerations

Why choose an infinite loop? The rationale lies in several factors:

1. Unreachability: The loop is intended as unreachachable code, assuming exit has successfully terminated the program.
2. Breadth of Failure: By causing a segmentation fault, the loop can handle failures in cases where even nil dereference attempts are unsuccessful.
3. Recursion Prevention: Using recursion could lead to further error conditions, making a simple loop a more reliable solution.

Additional Unreachable Code

Similar arrangements appear in other sections of the runtime, including the finalization of fatal panics in panic.go. These ensure proper termination in the face of severe errors.

Implications

This seemingly insignificant infinite loop plays a vital role in the robustness of Go's runtime. By providing a failsafe mechanism, it safeguards against unexpected program behavior, ensuring a clean and controlled termination when all else fails.