more defensive sleep

src/textual/_win_sleep.py

@@ -1,54 +1,69 @@
-import ctypes
-from ctypes.wintypes import LARGE_INTEGER
+"""
+A version of `time.sleep` that is more accurate than the standard library (even on Python 3.11).
+
+This should only be imported on Windows.
+
+"""
+
 from time import sleep as time_sleep
 
 
 __all__ = ["sleep"]
 
-kernel32 = ctypes.windll.kernel32
 
 INFINITE = 0xFFFFFFFF
 WAIT_FAILED = 0xFFFFFFFF
 CREATE_WAITABLE_TIMER_HIGH_RESOLUTION = 0x00000002
 
+try:
+    import ctypes
+    from ctypes.wintypes import LARGE_INTEGER
 
-def sleep(sleep_for: float) -> None:
-    """A replacement sleep for Windows.
+    kernel32 = ctypes.windll.kernel32
+except Exception:
+    sleep = time_sleep
+else:
 
-    Python 3.11 added a more accurate sleep. This may be used on < Python 3.11
+    def sleep(secs: float) -> None:
+        """A replacement sleep for Windows.
 
-    Args:
-        sleep_for (float): Seconds to sleep for.
-    """
+        Note that unlike `time.sleep` this *may* sleep for slightly less than the
+        specified time. This is generally not an issue for Textual's use case.
 
-    # Subtract a millisecond to account for overhead
-    sleep_for = max(0, sleep_for - 0.001)
-    if sleep_for < 0.0005:
-        # Less than 0.5ms and its not worth doing the sleep
-        return
+        Args:
+            secs (float): Seconds to sleep for.
+        """
 
-    handle = kernel32.CreateWaitableTimerExW(
-        None,
-        None,
-        CREATE_WAITABLE_TIMER_HIGH_RESOLUTION,
-        0x1F0003,
-    )
-    if not handle:
-        time_sleep(sleep_for)
-        return
+        # Subtract a millisecond to account for overhead
+        sleep_for = max(0, secs - 0.001)
+        if sleep_for < 0.0005:
+            # Less than 0.5ms and its not worth doing the sleep
+            return
 
-    if not kernel32.SetWaitableTimer(
-        handle,
-        ctypes.byref(LARGE_INTEGER(int(sleep_for * -10_000_000))),
-        0,
-        None,
-        None,
-        0,
-    ):
-        kernel32.CloseHandle(handle)
-        time_sleep(sleep_for)
-        return
+        handle = kernel32.CreateWaitableTimerExW(
+            None,
+            None,
+            CREATE_WAITABLE_TIMER_HIGH_RESOLUTION,
+            0x1F0003,
+        )
+        if not handle:
+            time_sleep(sleep_for)
+            return
 
-    if kernel32.WaitForSingleObject(handle, INFINITE) == WAIT_FAILED:
-        time_sleep(sleep_for)
-    kernel32.CloseHandle(handle)
+        try:
+            if not kernel32.SetWaitableTimer(
+                handle,
+                ctypes.byref(LARGE_INTEGER(int(sleep_for * -10_000_000))),
+                0,
+                None,
+                None,
+                0,
+            ):
+                kernel32.CloseHandle(handle)
+                time_sleep(sleep_for)
+                return
+
+            if kernel32.WaitForSingleObject(handle, INFINITE) == WAIT_FAILED:
+                time_sleep(sleep_for)
+        finally:
+            kernel32.CloseHandle(handle)