talks / test-debug-prof.slide

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Testing, Debugging and Profiling
23 Apr 2013
Tags: go test profile debug

Fabrizio Milo, Miki Tebeka

* Testing

* Testing Recipe

- Write `test_<module>.go` (discovery based test system)
- With the same package as the one being tested
- import [[][testing]]
- Write `TestFoo(t`*testing.T)` functions
- Use `init` for setup
- Use `defer` for poor mans teardown (in *every* test function)
- Run `go`test`-v`
- Run `go`test`-run='.*Mul.*'`-v` to select tests
- Read `go`help`testflag` output for more options

* math.go

.code test-debug-prof/math/math.go

* math_test.go

.code test-debug-prof/math/math_test.go /START1/,/END1/

.code test-debug-prof/math/math_test.go /START2/,/END2/

* Table Driven Testing

.code test-debug-prof/table/math_test.go /START1/,/END1/

* Parallel Execution

.code test-debug-prof/parallel/math_test.go /START1/,/END1/

- `time`go`test` (~2sec)
- `time`go`test`-parallel`2` (~1sec)
- If you have CPU intensive tests try `go`test`-parallel`2`-cpu`2`

* Benchmarks

.code test-debug-prof/bench/math_test.go /START1/,/END1/

- `go`test`-bench`'.*'`

* Debugging

* GDB 7.5 on Mac 

- You need GDB 7.5 OS X has a branch of 6.X 

	$gdb --version

	GNU gdb (GDB) 7.5
	Copyright (C) 2012 Free Software Foundation, Inc.
	License GPLv3+: GNU GPL version 3 or later <>
	This is free software: you are free to change and redistribute it.
	There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
	and "show warranty" for details.
	This GDB was configured as "x86_64-apple-darwin11.4.2".
	For bug reporting instructions, please see:

* If you need to upgrade on OS X 

- Download latest stable release source code from

- Unpack and compile:

	tar xjvf gdb-7.4.tar.bz2
	cd gdb-7.4
	less gdb/README

- Sign GDB (more info in the link)


* Compiling go programs for debugging

- you can build a development version of dependent pkgs.

	go install -a -v -gcflags "-N -l" <pkgs-list>

Load GDB golang extensions:


* Gdb Configuration

    (gdb)source <go-installation>/src/pkg/runtime/ 
    (gdb)skip malloc.goc:436

you can add commands in your .gdbinit inside your GOPATH

	(GOPATH)$cat .gdbinit
	skip malloc.goc:436

* If GDB is properly configured for go if you read these lines:

.code test-debug-prof/debug/gdbout

* Let's use gdb on geodns:

	mkdir gdbex
	cd gdbex
	mkdir bin lib src
	export GOPATH=`pwd`
	brew install geoip # OSX
	yum install geoip-devel # RedHat / CentOs
	go get
	go build -a -v -gcflags "-N -l"


*  Configure Environment

- How to set an environemnt variable:

	set environment GOGCTRACE=1
	set environmnet GOMAXPROCS=1
	set environment GOTRACEBACK=2

note that we can add these variables to the `.gdbinit` file as well

- How to set arguments:

	set args -port=5300

* Breakpoints

- Breakpoint on module function:

	(gdb) b main.main

- Breakpoint on file line:

	(gdb) b serve.go:212

- Breakpoint on library function

	(gdb) b net/http.ListenAndServe

* How to inspect variables

- info locals  // locals only 
- info variables  // all variables including globals / static
- info args
- whatis <variablename>
- info variables <regexp>
- p <variablename>

* GDB Commands

- list
- list line

- list file.go:line
- break line
- break file.go:line
- disas

* Go Extensions (2)

- bt
- frame n
- p var
- p $len(var)
- p $dtype(var)
- iface var

- info goroutines
- goroutine n cmd
- help goroutine

* NOTE: You can't call a Go function

	(gdb) call 'main.greet'("hello")
	infrun.c:5777: internal-error: normal_stop: Assertion `get_frame_type (frame) == DUMMY_FRAME' failed.
	A problem internal to GDB has been detected,
	further debugging may prove unreliable.
	Quit this debugging session? (y or n) y

This is due to the differences on how Go calls a function and the way GDB does

* User Interfaces for GDB

- gdb -tui
- ddd
- Affinic's

* Hopwatch

.play test-debug-prof/hopwatch.go

* Go Manual

- import "runtime/debug"


	func PrintStack()


	func Stack(buf []byte, all bool) int

- import "runtime"


	func Breakpoint()

* Example

.code test-debug-prof/debug/break.go

* Custom Exceptions: Extending Error's interface


* Profiling
* Running the Memory Profiler

* Notes

in pre Go 1.0 the memory profiler requires that the garbage collection has run at least once.
To force the GC use runtime.GC() i.e:

	runtime.GC() // force Garbage Collection

The value of runtime.MemProfileRate is important to tweak as it adjusts the granularity of the stats, the default is to only consider allocations of 512kb or bigger. 


	go tool pprof <Executable>

install graphviz


* Testing References

- [[][testing]]
- [[][Testing]] section in "How To Write Go Code"
- [[][gocheck]]
- [[][go2xunit]] Jenkins integration

* Debugging References

- [[][gdb]]
- [[][Visual GDB Debugger]]
- [[][HopWatch]]