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1c0557c638
This commit conceptually reverts4c8ab10. Said commit was meant to prevent the scenario where memory-only permits -- those that don't pass admission but still consume memory -- completely prevent the admission of reads, possibly even causing a deadlock because a permit might even blocks its own admission. The protection introduced by said commit however proved to be very problematic. It made the status of resources on the permit very hard to reason about and created loopholes via which permits could accumulate without tracking or they could even leak resources. Instead of continuing to patch this broken system, this commit does away with this "protection" based on the observation that deadlocks are now prevented anyway by the admission criteria introduced by0fe75571d9, which admits a read anyway when all the initial count resources are available (meaning no admitted reader is alive), regardless of availability of memory. The benefits of this revert is that the semaphore now knows about all the resources and is able to do its job better as it is not "lied to" about resource by the permits. Furthermore the status of a permit's resources is much simpler to reason about, there are no more loopholes in unexpected state transitions to swallow/leak resources. To prove that this revert is indeed safe, in the next commit we add robust tests that stress test admission on a highly contested semaphore. This patch also does away with the registered/admitted differentiation of permits, as this doesn't make much sense anymore, instead these two are unified into a single "active" state. One can always tell whether a permit was admitted or not from whether it owns count resources anyway. (cherry picked from commitcaaa8ef59a)