proxy-io.h: Add Connection disconnect and waitDrained methods - #335
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ryanofsky wants to merge 3 commits into
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proxy-io.h: Add Connection disconnect and waitDrained methods#335ryanofsky wants to merge 3 commits into
disconnect and waitDrained methods#335ryanofsky wants to merge 3 commits into
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Split connection teardown out of ~Connection into an idempotent disconnect() method, with the destructor delegating to it. This is a behavior-neutral refactor: the same steps run in the same order on destruction. Having a separate disconnect() method allows severing a connection while keeping the Connection object alive, which the next commits use to let shutdown code wait for in-flight server call bodies to finish after a disconnect (bitcoin/bitcoin#35845). Two details are new: - disconnect() cancels the m_on_disconnect handlers before severing the connection. Previously they were implicitly canceled when the TaskSet member was destroyed. When disconnect() is called separately from destruction, this is required for correctness: severing the stream completes m_network.onDisconnect(), and the registered handlers (_Serve, ConnectStream) destroy the Connection object out from under the caller. - disconnect() explicitly releases m_thread_pool and m_thread_map so worker thread teardown happens at disconnect time whether or not the object is destroyed right away. Previously this happened implicitly during member destruction. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Add a per-connection ServerObjectTracker counting live ProxyServer objects, incremented in the ProxyServerBase constructor and decremented in its destructor, with Connection::waitDrained() blocking until the count reaches zero and Connection::pendingServerObjects() exposing it for logging. Disconnecting a connection cancels the KJ promise of an in-flight call, but a C++ server method body already dispatched to a worker thread runs to completion. Counting live server objects turns Cap'n Proto's object lifetime rules into a usable quiescence signal: a ProxyServer object is not destroyed until its outstanding calls finish (the target capability is kept alive for the duration of a call and pinned by post()/PassField via thisCap()), so after disconnect() the count drains to zero exactly when no server call body is still executing. Waiting for that lets shutdown code avoid freeing application state that a still-running call body dereferences (bitcoin/bitcoin#35845). The tracker is held via shared_ptr by the Connection and by every ProxyServer object because objects kept alive by in-flight calls can outlive the Connection on some teardown paths (see ~ProxyServerBase), and their destructors must decrement state that is still valid. It must be declared before m_rpc_system, whose construction creates the bootstrap server object that registers itself with the tracker. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Add a deterministic mptest regression test for bitcoin/bitcoin#35845: hold a server method body in flight on a worker thread, call Connection::disconnect(), and assert that Connection::waitDrained() blocks until the body finishes and its server object is destroyed. Also covers destroying an already-disconnected connection (~Connection noticing disconnect() has run). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Add
ConnectionclassdisconnectandwaitDrainedmethods to provide more flexibility when forcibly disconnecting from remote clients or servers.Without these methods, the only way to forcibly close IPC connections is to delete
Connectionobjects. This works but is not ideal because once aConnectionobject is gone, it is difficult to track state still associated with the connection, particularly:ProxyServerobjects that may still be alive because they are executing asynchronous requests made before the disconnect. Without a way to track these objects, there is no generic way to wait for requests to finish existing after disconnecting. So individual IPC interfaces like the Bitcoin mining interface would need to implement custom synchronization to avoid race conditions during shutdown. Followup PR ipc: make ipc::disconnectIncoming wait for in-progress calls to complete bitcoin/bitcoin#35932 builds on this PR, calling the newwaitDrainedmethod introduced here to avoid IPC mining crashes on Bitcoin core shutdown without needing to change the mining code. A unit test is added here simulating these mining crashes.ProxyClientobjects that contain pointers toConnectionobjects. CurrentlyProxyClientobject need to register cleanup handlers withConnectionobjects to deal with Connections being deleted, which consumes memory and complicatesProxyClientshutdown logic. After this change, a followup PR will drop the cleanup handlers soConnectionobjects no longer need to track lists ofProxyClientobjects associated with them. This is implemented in proxy-io: Reference-count Connection objects #336.