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test: show QueryContext cancel/Scan race condition #706

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44 changes: 44 additions & 0 deletions go18_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,10 @@ import (
"database/sql"
"database/sql/driver"
"errors"
"math/rand"
"runtime"
"strings"
"sync"
"testing"
"time"

Expand Down Expand Up @@ -161,6 +163,48 @@ func TestContextCancelQuery(t *testing.T) {
}
}

// TestContextCancelQueryWhileScan checks for race conditions that arise when
// a query context is canceled while a user is calling rows.Scan(). The code
// is based on database/sql TestIssue18429.
// See https://github.com/golang/go/issues/23519
func TestContextCancelQueryWhileScan(t *testing.T) {
db := openTestConn(t)
defer db.Close()

const milliWait = 30
sem := make(chan bool, 20)

// This query seems to work well for triggering race conditions between
// the rows.Scan() call below, and the implicit rows.Close() call triggered
// by ctx timing out.
sql := `SELECT (g/10)::int, json_agg(g) FROM generate_series(1, 1000) g, pg_sleep($1) GROUP BY 1;`
var wg sync.WaitGroup
for i := 0; i < contextRaceIterations; i++ {
sem <- true
wg.Add(1)
go func() {
defer func() {
<-sem
wg.Done()
}()
qwait := float64(time.Duration(rand.Intn(milliWait))*time.Millisecond) / 1000

ctx, cancel := context.WithTimeout(context.Background(), time.Duration(rand.Intn(milliWait))*time.Millisecond)
defer cancel()
rows, _ := db.QueryContext(ctx, sql, qwait)
if rows != nil {
var d int
var n string
for rows.Next() {
rows.Scan(&d, &n)
}
rows.Close()
}
}()
}
wg.Wait()
}

// TestIssue617 tests that a failed query in QueryContext doesn't lead to a
// goroutine leak.
func TestIssue617(t *testing.T) {
Expand Down