Dtrace probes in your Golang code

goarena.go

package main

/*
Ping vs Pong: A Gladiatorial Match
Two goroutines enter, only one leaves...
*/

/*
#cgo LDFLAGS: -lprobes -L/usr/local/lib
#include "probes.h"
*/
import "C"

import (
  "time"
  "math/rand"
)

func ping(c chan int, q chan int) {
  for ;; {
    // Prepare a swing
    time.Sleep(time.Duration(rand.Intn(5)) * time.Second)
    n := <- c
    n += 1

    if n == 10 {
      q <- 0
    }

    c <- n
    // Dtrace spectators: roar for Ping!
    C.Ping(C.int(n))
  }
}

func pong(c chan int, q chan int) {
  for ;; {
    // Charge an attack
    time.Sleep(time.Duration(rand.Intn(5)) * time.Second)
    n := <- c
    n -= 1

    if n == 0 {
      q <- 1
    }

    c <- n
    // Dtrace spectators: cheer for Pong!
    C.Pong(C.int(n))
  }
}

func main() {
  c := make(chan int, 2)
  q := make(chan int)

  // Ping and Pong enter the arena
  go ping(c, q)
  go pong(c, q)

  // The match starts!
  c <- 5

  // Wait for victor signal
  winner := <- q

  if winner == 0 {
    println("After a long and arduous battle, Pong falls to its knees, its body a weary mess. Ping wins!")
  } else {
    println("Overcome by one too many wounds, Ping rushes to the ground. Pong wins!")
  }
}

probes.c

/*
  Compile probes.c as a shared library
  In Mac OS X (http://www.finkproject.org/doc/porting/shared.php#build-lib):
  cc -fno-common -c probes.c
  cc -dynamiclib -install_name /usr/local/lib/libprobes.dylib -o libprobes.dylib probes.o
  cp libprobes.dylib /usr/local/lib/
*/
#include "probes.h"

void Ping(int n) {
  GOLANG_PING(n);
}

int Ping_enabled() {
  return GOLANG_PING_ENABLED();
}

void Pong(int n) {
  GOLANG_PONG(n);
}

int Pong_enabled() {
  return GOLANG_PONG_ENABLED();
}

probes.d

/* 
  Generate probes.h header file with:
  dtrace -o probes.h -h -s probes.d
*/
provider golang {
  probe ping(int);
  probe pong(int);
};

probes.h

/* Header file generated by dtrace */
/* ... */

/* probes.c functions */
void Ping(int);
int  Ping_enabled();
void Pong(int);
int  Pong_enabled();

spectator.d

golang*::Ping:
{
    printf("Ping hits, counter goes up to #%d!", arg0);
}

golang*::Pong:
{
    printf("Pong connects, counter goes down to #%d!", arg0);
}

Demo of static Dtrace probes in Golang. Run with go run goarena.go, spectate with sudo dtrace -s spectator.d.

I failed at making Golang's cgo work nicely with a static library, which is why probes.c needs to be compiled as a shared library. Otherwise, dtrace's probe.h file could have been used directly.

Golang bindings for Chris Andrew's libusdt would probably allow more user-friendly dtrace probes in similar programs.