Bugfix: Closing PostgreSQL connection deadlocks listen(_:)

[billyean]

Received the following diagnostics while designing an application with postgres-nio 1.27.0...1.29.0:

00:56:35.221 [NotificationsListener.swift:517] - Notifications: Failed to LISTEN {error: "PSQLError(code: server, serverInfo: [sqlState: 57P01, file: be-secure.c, line: 209, message: terminating connection due to unexpected postmaster exit, routine: secure_read, localizedSeverity: FATAL, severity: FATAL])", topic: hawq_39}
00:56:35.222 [PostgresChannelHandler.swift:104] - Channel error caught. {psql_error: "I/O on closed channel", psql_connection_id: "1"}
00:56:35.222 [NotificationsListener.swift:286] - Notifications: Restarting subscription {topic: hawq_205}
00:56:35.222 [NotificationsListener.swift:148] - Notifications: Starting listening {psql.conn.id: "0", psql.conn.isClosed: true, topic: hawq_157}

SWIFT TASK CONTINUATION MISUSE: listen(_:) leaked its continuation without resuming it. This may cause tasks waiting on it to remain suspended forever.

And then the application deadlocks because listen() doesn't ever return.

Reproduction:

1. The code looks like that:

            try await self.postgresClient.withConnection { connection in
                148: log.debug("Notifications: Starting listening", metadata: [       
                    "topic": "\(topic)",                                         
                    "psql.conn.id": "\(connection.id)",                          
                    "psql.conn.isClosed": "\(connection.isClosed)"               
                ])                                                               
                sequence = try await connection.listen(topic.stringValue)        
                154: log.debug("Notifications: Now listening", metadata: [            
                    "topic": "\(topic)",                                          
                    "psql.conn.id": "\(connection.id)",                          
                    "psql.conn.isClosed": "\(connection.isClosed)"               
                ])
   

2. brew services restart postgresql

3. The error log similar to the log above gets generated, and the system goes into a deadlock.

Notice the log from line 148 is present, the connection appears to be CLOSED, and then the line 154 is unreachable. This might mean that listen() state machine is not correct on closed channels and result in deadlock.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.84%. Comparing base (4795a0b) to head (617dd6d).

Files with missing lines	Patch %	Lines
...es/PostgresNIO/Connection/PostgresConnection.swift	50.00%	3 Missing ⚠️
Sources/PostgresNIO/New/NotificationListener.swift	75.00%	2 Missing ⚠️
.../Connection State Machine/ListenStateMachine.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #600      +/-   ##
==========================================
- Coverage   62.51%   60.84%   -1.68%     
==========================================
  Files         132      132              
  Lines       10424     9540     -884     
==========================================
- Hits         6517     5805     -712     
+ Misses       3907     3735     -172     

Files with missing lines	Coverage Δ
...urces/PostgresNIO/New/PostgresChannelHandler.swift	83.71% <100.00%> (-0.78%)	⬇️
.../Connection State Machine/ListenStateMachine.swift	65.67% <0.00%> (-3.37%)	⬇️
Sources/PostgresNIO/New/NotificationListener.swift	68.23% <75.00%> (-4.89%)	⬇️
...es/PostgresNIO/Connection/PostgresConnection.swift	40.05% <50.00%> (-0.54%)	⬇️

... and 78 files with indirect coverage changes

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