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Implement driver.Pinger #565

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Implement driver.Pinger #565

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4a32ba5
Implement driver.Pinger
edsrzf Apr 2, 2017
6b890cc
Ping reads its result; obeys the context's Done channel
edsrzf Apr 4, 2017
093e458
Ping can cancel while waiting for a response
edsrzf Apr 7, 2017
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24 changes: 24 additions & 0 deletions connection_go18.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
// +build go1.8

package mysql

import (
"context"
)

func (mc *mysqlConn) Ping(ctx context.Context) error {
err := mc.writeCommandPacket(comPing)
if err != nil {
return err
}

select {
case <-ctx.Done():
mc.Close()
return ctx.Err()
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This is dangerous.

  • mc is not thread safe.
  • mc.readResultOK() is still working.
  • After Ping return, database/sql.DB will use this connection again. race may be happen.

default:
}

_, err = mc.readResultOK()
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This code didn't cancel waiting OK package when ctx is canceled.

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I'm not sure what you mean. Are you saying we should still read the OK result after the Done channel is closed? If so, what's the point if we're closing the connection anyway? And if not, please explain more.

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No. readResultOK() waits OK packet from MySQL server. It may take long time.
While waiting OK packet, context can be cancelled. Then, driver should abandon waiting OK.

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@edsrzf edsrzf Apr 6, 2017 •
edited
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So are you looking for something like this, then?

ch := make(chan err)
go func() {
    _, err = mc.readResultOK()
   ch <- err
}()
select {
case <-ctx.Done():
    mc.Close()
    return ctx.Err()
case err := <- ch:
    return err
}

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Yes

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FYI, this is how to interrupt conn.Read().
https://github.com/cybozu-go/cmd/blob/21e6f5953122316b450289d4e20fb664d84ffe41/http.go#L226
(thanks to @ymmt2005)

return err
}
17 changes: 17 additions & 0 deletions driver_go18_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,9 @@
package mysql

import (
"context"
"database/sql"
"database/sql/driver"
"fmt"
"reflect"
"testing"
Expand Down Expand Up @@ -188,3 +190,18 @@ func TestSkipResults(t *testing.T) {
}
})
}

func TestPing(t *testing.T) {
runTests(t, dsn, func(dbt *DBTest) {
mysqlDriver := dbt.db.Driver().(driver.Driver)
conn, err := mysqlDriver.Open(dsn)
if err != nil {
dbt.Fatalf("error opening conn: %s", err)
}
pinger := conn.(driver.Pinger)
err = pinger.Ping(context.Background())
if err != nil {
dbt.Fatalf("error on ping: %s", err)
}
})
}