wait until processImpl completes before closing stream chan

[nmerkulov]

Fix race condition in query processing

Problem

There was a race condition between closing the stream channel and writing to it from a background goroutine in conn_query.go.

Race condition scenario:

1. conn_query.go starts a goroutine that calls c.process(ctx, onProcess) (line 45)
2. c.process() spawns another goroutine internally that calls c.processImpl() (line 106 in conn_process.go)
3. c.processImpl() reads data from the server and calls on.data(block) for each data block (line 170 in conn_process.go)
4. When the context is cancelled, c.process() returns with ctx.Err()
5. The outer goroutine in conn_query.go immediately closes the stream channel (line 54)
6. However, the inner goroutine from step 2 may still be running and attempting to write to stream via on.data(block)
7. Writing to a closed channel causes a panic: panic: send on closed channel

Stack trace example:

goroutine 1: close(stream)
goroutine 2: stream <- b  // panic!

Solution

Modified conn_process.go to ensure that the process() function waits for the internal goroutine to complete before returning, even when the context is cancelled.

Changes:

• When ctx.Done() is triggered, after calling c.cancel(), we now wait for the goroutine to finish by selecting on errCh or doneCh
• This guarantees that on.data will not be called after process() returns
• The stream channel can now be safely closed in conn_query.go without race conditions

Impact

• Fixes panic when cancelling queries that are actively receiving data
• Ensures proper cleanup and resource management
• No breaking changes to public API
• Minimal performance impact (only adds synchronization on context cancellation path)

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull Request Overview

This PR fixes a race condition in query processing where the stream channel could be closed while a background goroutine was still attempting to write to it, causing a panic.

• Adds synchronization to wait for background goroutine completion before returning from process() function when context is cancelled
• Prevents "send on closed channel" panic during query cancellation
• Ensures proper cleanup and resource management without breaking API changes

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[Copilot]

Corrected spelling of 'untill' to 'until' in the PR title.

[kavirajk]

@nmerkulov thanks for the PR :) do you mind adding a test case to lock the behavior?