The Standard ML Basis Library

The `Timer` structure

Synopsis

signature TIMER structure Timer :> TIMER

The Timer structure provides facilities for measuring the passing of wall clock (real) time and the amount of time the running process has had the CPU (user time), has been active in the OS kernel (system time), and has spent on garbage collection (GC time).

Interface

type cpu_timer type real_timer val startCPUTimer : unit -> cpu_timer val checkCPUTimer : cpu_timer -> {usr : Time.time, sys : Time.time} val checkGCTime : cpu_timer -> Time.time val totalCPUTimer : unit -> cpu_timer val startRealTimer : unit -> real_timer val checkRealTimer : real_timer -> Time.time val totalRealTimer : unit -> real_timer

Description

type cpu_timer type real_timer

Type real_timer is the type of wall clock (real) timers, and cpu_timer is the type of CPU timers.

val startCPUTimer : unit -> cpu_timer

This returns a CPU timer that measures the time the process is computing (has control of the CPU) starting at this call.

checkCPUTimer ct

returns the user time (usr) and system time (sys) that have accumulated since the timer ct was started. Note that implementations should include any time spent in the garbage collector in the usr time component.

checkGCTime ct

returns the GC time that has accumulated since the timer ct was started. This function can be used in conjunction with checkCPUTimer to determine the non-GC user time as follows:

fun userTime ct = let
      val {usr, ...} = Timer.checkCPUTimer ct
      in
        Time.- (usr, Timer.checkGCTime ct)
      end

val totalCPUTimer : unit -> cpu_timer

This returns a CPU timer that measures the time the process is computing (has control of the CPU) starting at some system-dependent initialization time.

val startRealTimer : unit -> real_timer

This returns a wall clock (real) timer that measures how much time passes, starting from the time of this call.

checkRealTimer rt

returns the amount of (real) time that has passed since the timer rt was started.

val totalRealTimer : unit -> real_timer

This returns a wall clock (real) timer that measures how much time passes, starting from some system-dependent initialization time.

Discussion

The accuracy of the user, system, and GC times depends on the resolution of the system timer and the function call overhead in the OS interface. In particular, very small intervals might not be reported accurately.

On a Unix system, the user and system time reported by a CPU timer do not include the time spent in child processes.

Implementation note:

Some operating systems may lack the ability to measure CPU time consumption, in which case the real time should be returned instead.

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Generated October 02, 2003
Last Modified October 31, 1997
Comments to John Reppy.

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