Arithmetic overflow when recording mailboxCount metric during shutdown #802
Description
It appears that in some cases an actor's Mailbox can shut down with more processedActivations than initial messages for a given run. This results in an arithmetic error when trying to record the mailboxCount metric when the mailbox is shutting down:
0x7f10e50fa97f 0x55d9e6c13c4f, Swift runtime failure: arithmetic overflow at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/Mailbox.swift:0 0x55d9e6c13c4f, DistributedActors.Mailbox.(mailboxRun in _F5A1B51A24FD9930199EBF91BB3C2562)(DistributedActors.ActorShell<A>) -> DistributedActors.Mailbox<A>.(MailboxRunResult in _F5A1B51A24FD9930199EBF91BB3C2562) at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/Mailbox.swift:489 0x55d9e6c12208, DistributedActors.Mailbox.run() -> () at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/Mailbox.swift:333 0x55d9e6997a66, reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_guaranteed () -> (@out ()) at /workspace/<compiler-generated>:0 0x55d9e6bfae0d, partial apply forwarder for reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_guaranteed () -> (@out ()) at /workspace/<compiler-generated>:0 0x55d9e6bfb1b9, reabstraction thunk helper from @escaping @callee_guaranteed () -> (@out ()) to @escaping @callee_guaranteed () -> () at .build/checkouts/swift-distributed-actors/Sources/DistributedActors/locks.swift:0 0x55d9e6bfb1b9, closure #1 () -> () in DistributedActors.FixedThreadPool.init(Swift.Int) throws -> DistributedActors.FixedThreadPool at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/FixedThreadPool.swift:75 0x55d9e6cbc969, closure #1 () -> () in DistributedActors.Thread.init(() -> ()) throws -> DistributedActors.Thread at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/Thread.swift:53 0x55d9e6cbc969, partial apply forwarder for closure #1 () -> () in DistributedActors.Thread.init(() -> ()) throws -> DistributedActors.Thread at /workspace/<compiler-generated>:0 0x55d9e6cbc45f, closure #1 (Swift.Optional<Swift.UnsafeMutableRawPointer>) -> Swift.Optional<Swift.UnsafeMutableRawPointer> in static DistributedActors.Thread.runnerCallback.getter : @convention(c) (Swift.Optional<Swift.UnsafeMutableRawPointer>) -> Swift.Optional<Swift.UnsafeMutableRawPointer> at /workspace/.build/checkouts/swift-distributed-actors/Sources/DistributedActors/Thread.swift:132 0x7f10e50ef6da 0x7f10e327e71e 0xffffffffffffffff We can add a mitigation for this behavior while investigating the root cause that is triggering it.