fix(pool): double freeturn bug

[ndyakov]

A regression was reported where with aggressive timeout configuration the pool was stuck. Traced back to #3518

This PR fixes #3619 and #3623

[ndyakov]

@cyningsun feel free to review if you can.

[Copilot]

Pull request overview

This PR fixes a critical double-free bug in the connection pool that caused the pool to get stuck with aggressive timeout configurations. The bug occurred when a dial goroutine created a connection, the original waiter timed out, and the connection was delivered to another waiter - both the dial goroutine and the recipient would call freeTurn(), causing the semaphore to be released twice and allowing more concurrent operations than the pool size permits.

Key Changes

• Added gotConn atomic boolean to track whether a waiter successfully received a connection
• Modified dial goroutine logic to conditionally call freeTurn() based on whether the original waiter received a connection
• Enhanced context timeout handling in redis.go to respect caller deadlines during connection initialization waits
• Added comprehensive test coverage for the double-free scenario

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
redis.go	Enhanced timeout logic to use minimum of remaining command timeout and DialTimeout when waiting for connection initialization
internal/pool/want_conn.go	Added atomic gotConn field to track whether waiter received a connection, enabling proper turn management
internal/pool/pool.go	Modified dial goroutine to conditionally free turns based on waiter's connection receipt status, preventing double-free
internal/pool/double_freeturn_test.go	Added test demonstrating the double-free bug scenario with slow dials and timeouts
internal/pool/double_freeturn_simple_test.go	Added simple test to detect double-free by checking queue length during critical window

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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

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[cyningsun]

Thanks for the excellent work @ndyakov! Your test coverage and solution look comprehensive.

I've prepared #3626 as an alternative approach focusing on turn ownership semantics. It's offered in case it provides any additional useful insights, but please feel free to close it if #3625 already covers all the necessary ground.

[ndyakov]

#3626 was merged instead