feat: add cython monotonic_time_coarse implementation (#38)

build_ext.py

@@ -18,6 +18,14 @@
     language="c",
 )
 
+time_module = Extension(
+    "bluetooth_data_tools._time_impl",
+    [
+        join("src", "bluetooth_data_tools", "_time_impl.pyx"),
+    ],
+    language="c",
+)
+
 
 class BuildExt(build_ext):
     def build_extensions(self) -> None:
@@ -36,7 +44,7 @@ def build(setup_kwargs: Any) -> None:
         setup_kwargs.update(
             dict(
                 ext_modules=cythonize(
-                    [utils_module, "src/bluetooth_data_tools/gap.py"],
+                    [time_module, utils_module, "src/bluetooth_data_tools/gap.py"],
                     compiler_directives={"language_level": "3"},  # Python 3
                 ),
                 cmdclass=dict(build_ext=BuildExt),

src/bluetooth_data_tools/__init__.py

@@ -11,6 +11,7 @@
     parse_advertisement_data_tuple,
 )
 from .privacy import get_cipher_for_irk, resolve_private_address
+from .time import monotonic_time_coarse
 from .utils import int_to_bluetooth_address
 
 __version__ = "1.15.0"
@@ -31,6 +32,7 @@
     "calculate_distance_meters",
     "get_cipher_for_irk",
     "resolve_private_address",
+    "monotonic_time_coarse",
 ]
 
 

src/bluetooth_data_tools/_time_impl.pyx

@@ -0,0 +1,11 @@
+import cython
+
+from posix.time cimport clock_gettime, timespec
+
+
+def _monotonic_time_coarse():
+    cdef timespec ts
+    cdef double current
+    clock_gettime(6, &ts)
+    current = ts.tv_sec + (ts.tv_nsec / 1000000000.)
+    return current

src/bluetooth_data_tools/time.py

@@ -0,0 +1,49 @@
+"""Bluetooth time utils."""
+from __future__ import annotations
+
+import platform
+import time
+from contextlib import suppress
+from functools import partial
+
+CLOCK_MONOTONIC_COARSE = 6
+
+
+def __gen_monotonic_time_coarse() -> partial[float]:
+    """Return a function that provides monotonic time in seconds.
+
+    This is the coarse version of time_monotonic, which is faster but less accurate.
+
+    Since many arm64 and 32-bit platforms don't support VDSO with time.monotonic
+    because of errata, we can't rely on the kernel to provide a fast
+    monotonic time.
+
+    https://lore.kernel.org/lkml/[email protected]/
+    """
+    # We use a partial here since its implementation is in native code
+    # which allows us to avoid the overhead of the global lookup
+    # of CLOCK_MONOTONIC_COARSE.
+    return partial(time.clock_gettime, CLOCK_MONOTONIC_COARSE)
+
+
+monotonic_time_coarse = time.monotonic
+_USE_COARSE_MONOTONIC_TIME = False
+
+with suppress(Exception):
+    if (
+        platform.system() == "Linux"
+        and abs(time.monotonic() - __gen_monotonic_time_coarse()()) < 1
+    ):
+        monotonic_time_coarse = __gen_monotonic_time_coarse()
+        _USE_COARSE_MONOTONIC_TIME = True
+
+if _USE_COARSE_MONOTONIC_TIME:
+    with suppress(ImportError):
+        from ._time_impl import (  # type: ignore[no-redef] # noqa: F811 F401
+            _monotonic_time_coarse as monotonic_time_coarse,
+        )
+
+
+__all__ = [
+    "monotonic_time_coarse",
+]