Prevent panics caused by attempting to close an already closed pgxpool.Pool.

pgxpool/pool.go

@@ -326,8 +326,14 @@ func ParseConfig(connString string) (*Config, error) {
 // Close closes all connections in the pool and rejects future Acquire calls. Blocks until all connections are returned
 // to pool and closed.
 func (p *Pool) Close() {
+	// Check to see if the closeChan is closed before attempting to close it again, which can result in a panic.
+	select {
+	case <-p.closeChan:
+		// NOOP because the channel is already closed.
+	default:
 		close(p.closeChan)
 		p.p.Close()
+	}
 }
 
 func (p *Pool) backgroundHealthCheck() {

pgxpool/pool_test.go

@@ -789,3 +789,14 @@ func TestTxBeginFuncNestedTransactionRollback(t *testing.T) {
 	require.NoError(t, err)
 	require.EqualValues(t, 2, n)
 }
+
+func TestIdempotentPoolClose(t *testing.T) {
+	pool, err := pgxpool.Connect(context.Background(), os.Getenv("PGX_TEST_DATABASE"))
+	require.NoError(t, err)
+
+	// Close the open pool.
+	require.NotPanics(t, func() { pool.Close() })
+
+	// Close the already closed pool.
+	require.NotPanics(t, func() { pool.Close() })
+}