[Python-Dev] time.clock() on windows

Mark Hammond mhammond at skippinet.com.au
Thu Oct 22 12:57:53 CEST 2009

On 22/10/2009 8:47 PM, Kristján Valur Jónsson wrote:
> The point in question seems to be this this (from the thread):
>   * Need some sort of static "start value", which is set when the
>   process starts, so I can return to Python in seconds.  An easy hack
>   is to set this the first time clock() is called, but then it wont
>   reflect any sort of real time - but would be useful for relative
>   times...
> But the argumentation is flawed.

It was made in the context of the APIs available to implement this.  The 
code is short-and-sweet in timemodule.c, so please do go ahead and fix 
my flawed reasoning.

For reference:

#if defined(MS_WINDOWS) && !defined(__BORLANDC__)
/* Due to Mark Hammond and Tim Peters */
static PyObject *
time_clock(PyObject *self, PyObject *unused)
	static LARGE_INTEGER ctrStart;
	static double divisor = 0.0;
	double diff;

	if (divisor == 0.0) {
		if (!QueryPerformanceFrequency(&freq) || freq.QuadPart == 0) {
			/* Unlikely to happen - this works on all intel
			   machines at least!  Revert to clock() */
			return PyFloat_FromDouble(((double)clock()) /
		divisor = (double)freq.QuadPart;
	diff = (double)(now.QuadPart - ctrStart.QuadPart);
	return PyFloat_FromDouble(diff / divisor);



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