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gh-112567: Add _PyTimeFraction C API (#112568)

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Use a fraction internally in the _PyTime API to reduce the risk of
integer overflow: simplify the fraction using Greatest Common
Divisor (GCD). The fraction API is used by time functions:
perf_counter(), monotonic() and process_time().

For example, QueryPerformanceFrequency() usually returns 10 MHz on
Windows 10 and newer. The fraction SEC_TO_NS / frequency =
1_000_000_000 / 10_000_000 can be simplified to 100 / 1.

* Add _PyTimeFraction type.
* Add functions:

  * _PyTimeFraction_Set()
  * _PyTimeFraction_Mul()
  * _PyTimeFraction_Resolution()

* No longer check "numer * denom <= _PyTime_MAX" in
  _PyTimeFraction_Set(). _PyTimeFraction_Mul() uses _PyTime_Mul()
  which handles integer overflow.
This commit is contained in:
Victor Stinner 2023-12-01 19:50:10 +01:00 • committed by GitHub
parent 05a370abd6
commit 5c5022b862
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GPG key ID: 4AEE18F83AFDEB23
3 changed files with 130 additions and 107 deletions
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54
Modules/timemodule.c
View file

@ -69,25 +69,6 @@ module time
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=a668a08771581f36]*/
#if defined(HAVE_TIMES) || defined(HAVE_CLOCK)
static int
check_ticks_per_second(long tps, const char *context)
{
/* Effectively, check that _PyTime_MulDiv(t, SEC_TO_NS, tps)
cannot overflow. */
if (tps >= 0 && (_PyTime_t)tps > _PyTime_MAX / SEC_TO_NS) {
PyErr_Format(PyExc_OverflowError, "%s is too large", context);
return -1;
}
if (tps < 1) {
PyErr_Format(PyExc_RuntimeError, "invalid %s", context);
return -1;
}
return 0;
}
#endif /* HAVE_TIMES || HAVE_CLOCK */
/* Forward declarations */
static int pysleep(_PyTime_t timeout);
@ -96,11 +77,11 @@ typedef struct {
PyTypeObject *struct_time_type;
#ifdef HAVE_TIMES
// times() clock frequency in hertz
long ticks_per_second;
_PyTimeFraction times_base;
#endif
#ifdef HAVE_CLOCK
// clock() frequency in hertz
long clocks_per_second;
_PyTimeFraction clock_base;
#endif
} time_module_state;
@ -174,10 +155,11 @@ Return the current time in nanoseconds since the Epoch.");
static int
py_clock(time_module_state *state, _PyTime_t *tp, _Py_clock_info_t *info)
{
long clocks_per_second = state->clocks_per_second;
_PyTimeFraction *base = &state->clock_base;
if (info) {
info->implementation = "clock()";
info->resolution = 1.0 / (double)clocks_per_second;
info->resolution = _PyTimeFraction_Resolution(base);
info->monotonic = 1;
info->adjustable = 0;
}
@ -189,7 +171,7 @@ py_clock(time_module_state *state, _PyTime_t *tp, _Py_clock_info_t *info)
"or its value cannot be represented");
return -1;
}
_PyTime_t ns = _PyTime_MulDiv(ticks, SEC_TO_NS, clocks_per_second);
_PyTime_t ns = _PyTimeFraction_Mul(ticks, base);
*tp = _PyTime_FromNanoseconds(ns);
return 0;
}
@ -1257,7 +1239,7 @@ static int
process_time_times(time_module_state *state, _PyTime_t *tp,
_Py_clock_info_t *info)
{
long ticks_per_second = state->ticks_per_second;
_PyTimeFraction *base = &state->times_base;
struct tms process;
if (times(&process) == (clock_t)-1) {
@ -1266,14 +1248,14 @@ process_time_times(time_module_state *state, _PyTime_t *tp,
if (info) {
info->implementation = "times()";
info->resolution = _PyTimeFraction_Resolution(base);
info->monotonic = 1;
info->adjustable = 0;
info->resolution = 1.0 / (double)ticks_per_second;
}
_PyTime_t ns;
ns = _PyTime_MulDiv(process.tms_utime, SEC_TO_NS, ticks_per_second);
ns += _PyTime_MulDiv(process.tms_stime, SEC_TO_NS, ticks_per_second);
ns = _PyTimeFraction_Mul(process.tms_utime, base);
ns += _PyTimeFraction_Mul(process.tms_stime, base);
*tp = _PyTime_FromNanoseconds(ns);
return 1;
}
@ -1395,8 +1377,7 @@ py_process_time(time_module_state *state, _PyTime_t *tp,
// times() failed, ignore failure
#endif
/* clock */
/* Currently, Python 3 requires clock() to build: see issue #22624 */
/* clock(). Python 3 requires clock() to build (see gh-66814) */
return py_clock(state, tp, info);
#endif
}
@ -2110,20 +2091,23 @@ time_exec(PyObject *module)
#endif
#ifdef HAVE_TIMES
if (_Py_GetTicksPerSecond(&state->ticks_per_second) < 0) {
long ticks_per_second;
if (_Py_GetTicksPerSecond(&ticks_per_second) < 0) {
PyErr_SetString(PyExc_RuntimeError,
"cannot read ticks_per_second");
return -1;
}
if (check_ticks_per_second(state->ticks_per_second, "_SC_CLK_TCK") < 0) {
if (_PyTimeFraction_Set(&state->times_base, SEC_TO_NS,
ticks_per_second) < 0) {
PyErr_Format(PyExc_OverflowError, "ticks_per_second is too large");
return -1;
}
#endif
#ifdef HAVE_CLOCK
state->clocks_per_second = CLOCKS_PER_SEC;
if (check_ticks_per_second(state->clocks_per_second, "CLOCKS_PER_SEC") < 0) {
if (_PyTimeFraction_Set(&state->clock_base, SEC_TO_NS,
CLOCKS_PER_SEC) < 0) {
PyErr_Format(PyExc_OverflowError, "CLOCKS_PER_SEC is too large");
return -1;
}
#endif