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fix race condition - library can become not ready before the event.wait() returns #740

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fix race condition - library can become not ready before the event.wait() returns #740

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10 changes: 9 additions & 1 deletion asab/library/service.py
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Original file line number Diff line number Diff line change
Expand Up @@ -169,18 +169,26 @@ async def wait_for_library_ready(self, timeout: int = None):
"""
Wait for the library to be ready.

After the ready edge event fires, re-checks `is_ready()`; if another task
moved the library back to not-ready before this coroutine resumed, raises
instead of waiting again.

Args:
timeout (int): The timeout in seconds. If not provided, the default timeout is used.

Raises:
LibraryNotReadyError: If the library is not ready within the timeout.
LibraryNotReadyError: If the library is not ready within the timeout, or if it is
not ready when this coroutine continues after the wait.
"""
if timeout is None:
timeout = self.LibraryReadyTimeout
if self.is_ready():
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@mithunbharadwaj mithunbharadwaj Mar 24, 2026

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Fast path is good. It avoids waiting when readiness already holds at entry itself.

return
try:
await asyncio.wait_for(self.LibraryReadyEvent.wait(), timeout=timeout)
except asyncio.TimeoutError:
raise LibraryNotReadyError("Library is not ready yet.")
self._ensure_ready()
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@mithunbharadwaj mithunbharadwaj Mar 24, 2026

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This still feels like a one-time wait. We wake on the first ready event and then decide immediately from that one wake-up.

If the goal is still “wait until ready or timeout”, I think we probably need to keep waiting when that wake turns out to be stale, instead of treating it as the final truth for readiness.

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@mithunbharadwaj mithunbharadwaj Mar 24, 2026

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I would probably do something like this instead, so we keep waiting until self.is_ready() is actually true, while still respecting the original timeout.


async def wait_for_library_ready(self, timeout: int = None):
    if timeout is None:
        timeout = self.LibraryReadyTimeout

    loop = asyncio.get_running_loop()
    deadline = loop.time() + timeout

    while True:
        if self.is_ready():
            return

        remaining = deadline - loop.time()
        if remaining <= 0:
            raise LibraryNotReadyError("Library is not ready yet.")

        try:
            await asyncio.wait_for(self.LibraryReadyEvent.wait(), timeout=remaining)
        except asyncio.TimeoutError:
            raise LibraryNotReadyError("Library is not ready yet.")


async def _set_ready(self, provider):
if len(self.Libraries) == 0:
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