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No blocking acquire on event loop - #2252
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Motivation: #2226 made the connection-permit acquire non-blocking on the event loop. CombinedConnectionSemaphore's non-blocking path takes the global permit first and then the per-host permit, releasing the global one if the per-host permit is unavailable. That releaseGlobal branch is the single place the non-blocking path can leak the global permit, yet it had no coverage: the existing combinedNonBlockingFailsFastWhenExhausted uses equal global and per-host limits (1, 1), so the acquire is rejected at the global gate and never reaches the per-host rejection where releaseGlobal runs. Modification: Add combinedNonBlockingReleasesGlobalPermitWhenPerHostExhausted using a wider global limit (2) than per-host (1). The non-blocking acquire passes the global gate, is rejected by the per-host limit (asserted as TooManyConnectionsPerHostException), and a follow-up non-blocking acquire for a different host must succeed; proving the global permit taken during the failed attempt was released rather than leaked. Result: The global-permit release path of the non-blocking combined acquire is now covered; a regression that leaked the global permit on per-host rejection would starve other hosts of the global permit and fail this test.
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Motivation:
#2226 made the connection-permit acquire non-blocking on the event loop. CombinedConnectionSemaphore's non-blocking path takes the global permit first and then the per-host permit, releasing the global one if the per-host permit is unavailable. That releaseGlobal branch is the single place the non-blocking path can leak the global permit, yet it had no coverage: the existing combinedNonBlockingFailsFastWhenExhausted uses equal global and per-host limits (1, 1), so the acquire is rejected at the global gate and never reaches the per-host rejection where releaseGlobal runs.
Modification:
Add combinedNonBlockingReleasesGlobalPermitWhenPerHostExhausted using a wider global limit (2) than per-host (1). The non-blocking acquire passes the global gate, is rejected by the per-host limit (asserted as TooManyConnectionsPerHostException), and a follow-up non-blocking acquire for a different host must succeed; proving the global permit taken during the failed attempt was released rather than leaked.
Result:
The global-permit release path of the non-blocking combined acquire is now covered; a regression that leaked the global permit on per-host rejection would starve other hosts of the global permit and fail this test.