Trace Mode

HPy’s trace mode allows you to analyze the usage of the HPy API. The two fundamental metrics are call count and duration. As the name already suggests, call count tells you how often a certain HPy API function was called and duration uses a monotonic clock to measure how much (accumulated) time was spent in a certain HPy API function. It is further possible to register custom on-enter and on-exit Python functions.

As with the debug mode, the trace mode can be activated at import time, so no recompilation is required.

Activating Trace Mode

Similar to how the debug mode is activated, use environment variable HPY. If HPY=trace, then all HPy modules are loaded with the trace context. Alternatively, it is also possible to specify the mode per module like this: HPY=modA:trace,modB=trace. Environment variable HPY_LOG also works.

Using Trace Mode

The trace mode can be accessed via the shipped module hpy.trace. It provides following functions:

  • get_call_counts() returns a dict. The HPy API function names are used as keys and the corresponding call count is the value.

  • get_durations() also returns a dict similar to get_call_counts but the value is the accumulated time spent in the corresponding HPy API function (in nanoseconds). Note, the used clock does not necessarily have a nanosecond resolution which means that the least significant digits may not be accurate.

  • set_trace_functions(on_enter=None, on_exit=None) allows the user to register custom trace functions. The function provided for on_enter and on_exit functions will be executed before and after and HPy API function is and was executed, respectively. Passing None to any of the two arguments or omitting one will clear the corresponding function.

  • get_frequency() returns the resolution of the used clock to measure the time in Hertz. For example, a value of 10000000 corresponds to 10 MHz. In that case, the two least significant digits of the durations are inaccurate.


Following HPy function uses HPy_Add:

HPyDef_METH(add, "add", HPyFunc_VARARGS)
static HPy add_impl(HPyContext *ctx, HPy self, HPy *args, HPy_ssize_t nargs)
    if (nargs != 2) {
        HPyErr_SetString(ctx, ctx->h_TypeError, "expected exactly two args");
        return HPy_NULL;
    return HPy_Add(ctx, args[0], args[1]);

When this script is executed in trace mode:

# Run with HPY=trace
from hpy.trace import get_call_counts
import snippets

add_count_0 = get_call_counts()["ctx_Add"]
snippets.add(1, 2) == 3
add_count_1 = get_call_counts()["ctx_Add"]

print('get_call_counts()["ctx_Add"] == %d' % (add_count_1 - add_count_0))

The output is get_call_counts()["ctx_Add"] == 1.