Go: Stack traces

A stack trace is the list of functions that the program was in the middle of when the stack trace was printed.

Stack traces are typically printed to the console when unexpected error occurs. They can be very useful for debugging:

  • not only do you see where the error happened,
  • but also how the program arrived in this place.

Example

goroutine 11 [running]: testing.tRunner.func1(0xc420092690) /usr/local/go/src/testing/testing.go:711 +0x2d2 panic(0x53f820, 0x594da0) /usr/local/go/src/runtime/panic.go:491 +0x283 github.com/yourbasic/bit.(*Set).Max(0xc42000a940, 0x0) ../src/github.com/bit/set_math_bits.go:137 +0x89 github.com/yourbasic/bit.TestMax(0xc420092690) ../src/github.com/bit/set_test.go:165 +0x337 testing.tRunner(0xc420092690, 0x57f5e8) /usr/local/go/src/testing/testing.go:746 +0xd0 created by testing.(*T).Run /usr/local/go/src/testing/testing.go:789 +0x2de

The stack trace can be read from the bottom up:

  • testing.(*T).Run has called testing.tRunner
  • …which has called bit.TestMax
  • …which has called bit.(*Set).Max
  • …which has called panic
  • …which has called testing.tRunner.func1

The indented lines show the source file and line number at which the function was called. The hexadecimal numbers refer to parameter values, including values of pointers and internal data structures. Stack Traces in Go has more details.

To print the stack trace for the current goroutine, use debug.PrintStack from package runtime/debug.

You can also examine the current stack trace programatically by calling runtime.Stack.

Level of detail

The GOTRACEBACK variable controls the amount of output generated when a Go program fails.

  • GOTRACEBACK=none omits the goroutine stack traces entirely.
  • GOTRACEBACK=single (the default) prints a stack trace for the current goroutine, eliding functions internal to the run-time system. The failure prints stack traces for all goroutines if there is no current goroutine or the failure is internal to the run-time.
  • GOTRACEBACK=all adds stack traces for all user-created goroutines.
  • GOTRACEBACK=system is like all but adds stack frames for run-time functions and shows goroutines created internally by the run-time.

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