Golang PoolConnection.Close方法代码示例

// executeFetchContext calls ExecuteFetch() on the given connection,
// while respecting Context deadline and cancellation.
func (mysqld *Mysqld) executeFetchContext(ctx context.Context, conn dbconnpool.PoolConnection, query string, maxrows int, wantfields bool) (*sqltypes.Result, error) {
	// Fast fail if context is done.
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	// Execute asynchronously so we can select on both it and the context.
	var qr *sqltypes.Result
	var executeErr error
	done := make(chan struct{})
	go func() {
		defer close(done)

		qr, executeErr = conn.ExecuteFetch(query, maxrows, wantfields)
	}()

	// Wait for either the query or the context to be done.
	select {
	case <-done:
		return qr, executeErr
	case <-ctx.Done():
		// If both are done already, we may end up here anyway because select
		// chooses among multiple ready channels pseudorandomly.
		// Check the done channel and prefer that one if it's ready.
		select {
		case <-done:
			return qr, executeErr
		default:
		}

		// The context expired or was cancelled.
		// Try to kill the connection to effectively cancel the ExecuteFetch().
		connID := conn.ID()
		log.Infof("Mysqld.executeFetchContext(): killing connID %v due to timeout of query: %v", connID, query)
		if killErr := mysqld.killConnection(connID); killErr != nil {
			// Log it, but go ahead and wait for the query anyway.
			log.Warningf("Mysqld.executeFetchContext(): failed to kill connID %v: %v", connID, killErr)
		}
		// Wait for the conn.ExecuteFetch() call to return.
		<-done
		// Close the connection. Upon Recycle() it will be thrown out.
		conn.Close()
		// ExecuteFetch() may have succeeded before we tried to kill it.
		// If ExecuteFetch() had returned because we cancelled it,
		// then executeErr would be an error like "MySQL has gone away".
		if executeErr == nil {
			return qr, executeErr
		}
		return nil, ctx.Err()
	}
}