fix(conn): conn to have state machine

[ndyakov]

• Add connection state tracking instead of multiple flags
• Resolve race conditions on handoff
• Improve pool performance

This PR fixes issues related to us having multiple different atomic flags in the pool connections for handoff, usability, etc. Since I tried to slightly changed the get and set operations of the pool, this correctness (which negatively impacted the performance in the first place) does not have real world drawbacks and improves developer experience.

[Copilot]

Pull Request Overview

This PR refactors connection management to use a state machine architecture, replacing the previous boolean flags (usable, Inited, used) with a formal state machine that provides better concurrency control and clearer state transitions.

Key Changes:

• Introduced a new ConnStateMachine with explicit states: CREATED → INITIALIZING → IDLE ⇄ IN_USE, with UNUSABLE for handoff/reauth operations
• Replaced atomic boolean flags with atomic state transitions using CAS operations and FIFO waiting queues
• Updated connection initialization logic to handle concurrent initialization attempts properly

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
internal/pool/conn_state.go	New file implementing the connection state machine with FIFO waiting queue
internal/pool/conn_state_test.go	Comprehensive tests for state machine transitions and concurrency
internal/pool/conn.go	Refactored connection to use state machine instead of boolean flags
internal/pool/pool.go	Updated pool operations to use state machine transitions
internal/pool/pool_single.go	Added comments explaining SingleConnPool's non-thread-safe nature
redis.go	Refactored initConn to handle state transitions and concurrent initialization
maintnotifications/pool_hook.go	Updated to check handoff state before usability
maintnotifications/pool_hook_test.go	Updated tests to use state machine API
maintnotifications/handoff_worker.go	Added call to clear handoff state before closing
maintnotifications/errors.go	Added new error type and documentation comments
internal/auth/streaming/pool_hook.go	Simplified reauth logic using state machine's AwaitAndTransition
internal/auth/streaming/pool_hook_state_test.go	New tests verifying reauth respects state machine

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[Copilot]

Pull Request Overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

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[Copilot]

Pull Request Overview

Copilot reviewed 34 out of 37 changed files in this pull request and generated 4 comments.

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[Copilot]

Corrected spelling of 'passwrd' to 'password'.

[Copilot]

Changed from rawConn.Read() to rawConn.Control(), but the function signature changed from returning bool to void. The return true statement was removed on line 48, which is correct. However, Control() should be used for operations that don't read/write, while Read() is for read operations. Using Recvfrom with MSG_PEEK is a read operation, so rawConn.Read() was semantically correct. Consider reverting to Read() or document why Control() is preferred here.

Suggested change

	if err := rawConn.Control(func(fd uintptr) {
	if err := rawConn.Read(func(fd uintptr) {

[Copilot]

Lines 163-164 contain redundant condition checking. Line 163 already checks opt.MaxActiveConns < opt.PoolSize, so the inner if on line 164 will always be true. This appears to be dead code or a logic error.

Suggested change

	if opt.MaxActiveConns < opt.PoolSize {
	opt.MaxActiveConns = opt.PoolSize
	}

[Copilot]

The CREATED state check on line 738 is not atomic relative to line 737. After the CAS fails on line 737, another thread could transition the connection from CREATED to another state before line 738 checks it, leading to incorrect behavior. This should use a CAS for CREATED as well: cn.stateMachine.state.CompareAndSwap(uint32(StateCreated), uint32(StateCreated)) or combine into a single atomic operation.

Suggested change

	cn.stateMachine.state.Load() == uint32(StateCreated)
	cn.stateMachine.state.CompareAndSwap(uint32(StateCreated), uint32(StateCreated))