python_gc_duration_seconds gone between 0.4 and 0.7

[gjcarneiro]

I have always found the python_gc_duration_seconds Histogram extremely useful to track down latency problems in Python caused by the GC. But this metric seems to have disappeared when I upgraded client_prometheus from 0.4 to 0.7. Any chance to get it back? Pretty please?

[gjcarneiro]

Looks like this disappeared when #371 got merged.

[gjcarneiro]

I end up just adding back simplified similar code into my app. In case anyone else needs it:

import gc
import time
from prometheus_client import Histogram


PYTHON_GC_DURATION = Histogram(
    "python_gc_duration_seconds",
    "Time spent in garbage collection",
    ["generation"],
)

_python_gc_times = {}
_gc_cb_active = False


def _python_gc_cb(phase, info):
    global _gc_cb_active
    try:
        if _gc_cb_active:
            return
        _gc_cb_active = True

        gen = info["generation"]
        if phase == "start":
            _python_gc_times[gen] = time.monotonic()
        if phase == "stop":
            delta = time.monotonic() - _python_gc_times[gen]
            PYTHON_GC_DURATION.labels(gen).observe(delta)
    finally:
        _gc_cb_active = False


gc.callbacks.append(_python_gc_cb)

At the risk of a deadlock, sure. But, to be honest, I have never experienced such a deadlock, I'll take my chances for now.