database/sql: fix deadlock test in prepare statement

The issue go#46783 correctly diagnosed the context timeout
caused an intermittent failure when the context was canceled
prior to the BeginTx call. However due to the asynchronous nature
of canceling a Tx through a context on fast systems, the tx.Prepare
also succeeded. On slower systems or if a time.Sleep was inserted
between the BeginTx and Prepare, the Prepare would fail.

Resolve this by moving the context cancel after the Prepare.
This will still trigger the deadlock which I tested locally.
In addition, I interspersed multiple time.Sleep calls and the
test still functioned.

Fixes #46852

Change-Id: I9cbf90d3c12b2555493a37799738772b615ae39d
Reviewed-on: https://go-review.googlesource.com/c/go/+/329830
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Bryan C. Mills <bcmills@google.com>

diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 7d1cb9b85a59bf48060f939cc6f861ea474cf01d..f771dee4a9772a37444ef9b65d27de9b12af887a 100644 (file)
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -2841,7 +2841,6 @@ func TestTxStmtDeadlock(t *testing.T) {
        ctx, cancel := context.WithCancel(context.Background())
        defer cancel()
        tx, err := db.BeginTx(ctx, nil)
-       cancel()
        if err != nil {
                t.Fatal(err)
        }
@@ -2850,6 +2849,7 @@ func TestTxStmtDeadlock(t *testing.T) {
        if err != nil {
                t.Fatal(err)
        }
+       cancel()
        // Run number of stmt queries to reproduce deadlock from context cancel
        for i := 0; i < 1e3; i++ {
                // Encounter any close related errors (e.g. ErrTxDone, stmt is closed)