次に、Dプログラの例readtrace.dを示します。

/* readtrace.d -- Display time spent in read() calls */

syscall::read:entry
{
  self->t = timestamp; /* Initialize a thread-local variable */
}

syscall::read:return
/self->t != 0/
{
  printf("%s (pid=%d) spent %d microseconds in read()\n",
  execname, pid, ((timestamp - self->t)/1000)); /* Divide by 1000 for microseconds */

  self->t = 0; /* Reset the variable */
}

例では、readtrace.dプログラムは、プロセスがread()システム・コールを起動するたびに、コマンド名、プロセスIDおよびコール継続時間をマイクロ秒で表示します。 変数self->tはスレッド・ローカルです。これは、システムでのスレッド実行のスコープ内にのみ存在することを意味します。 プログラムでは、プロセスがread()をコールするときにself->tのtimestampの値が記録され、コールが戻るときにtimestampの値からこの値が減算されます。 timestampの単位はナノ秒であるため、1000で除算して値をマイクロ秒で取得します。

このプログラムの実行結果は次のとおりです:

# dtrace -q -s readtrace.d
NetworkManager (pid=878) spent 10 microseconds in read()
NetworkManager (pid=878) spent 9 microseconds in read()
NetworkManager (pid=878) spent 2 microseconds in read()
in:imjournal (pid=815) spent 63 microseconds in read()
gdbus (pid=878) spent 7 microseconds in read()
gdbus (pid=878) spent 66 microseconds in read()
gdbus (pid=878) spent 63 microseconds in read()
irqbalance (pid=816) spent 56 microseconds in read()
irqbalance (pid=816) spent 113 microseconds in read()
irqbalance (pid=816) spent 104 microseconds in read()
irqbalance (pid=816) spent 91 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 63 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
irqbalance (pid=816) spent 61 microseconds in read()
sshd (pid=10230) spent 8 microseconds in read()
in:imjournal (pid=815) spent 6 microseconds in read()
sshd (pid=10230) spent 7 microseconds in read()
in:imjournal (pid=815) spent 5 microseconds in read()
sshd (pid=10230) spent 7 microseconds in read()
in:imjournal (pid=815) spent 6 microseconds in read()
sshd (pid=10230) spent 7 microseconds in read()
in:imjournal (pid=815) spent 5 microseconds in read()
^C