Revert "database/sql: add driver.ResetSessioner and add pool support"

This reverts commit 2620ac3aea.

Reason for revert: broke all the builds.

Change-Id: I26fc09a13f5f80fa708de66c843442ff9d934694
Reviewed-on: https://go-review.googlesource.com/73050
Reviewed-by: Russ Cox <rsc@golang.org>

src/database/sql/sql.go

@@ -334,7 +334,6 @@ type DB struct {
 	// It is closed during db.Close(). The close tells the connectionOpener
 	// goroutine to exit.
 	openerCh    chan struct{}
-	resetterCh  chan *driverConn
 	closed      bool
 	dep         map[finalCloser]depSet
 	lastPut     map[*driverConn]string // stacktrace of last conn's put; debug only
@@ -342,8 +341,6 @@ type DB struct {
 	maxOpen     int                    // <= 0 means unlimited
 	maxLifetime time.Duration          // maximum amount of time a connection may be reused
 	cleanerCh   chan struct{}
-
-	stop func() // stop cancels the connection opener and the session resetter.
 }
 
 // connReuseStrategy determines how (*DB).conn returns database connections.
@@ -371,7 +368,6 @@ type driverConn struct {
 	closed      bool
 	finalClosed bool // ci.Close has been called
 	openStmt    map[*driverStmt]bool
-	lastErr     error // lastError captures the result of the session resetter.
 
 	// guarded by db.mu
 	inUse      bool
@@ -380,7 +376,7 @@ type driverConn struct {
 }
 
 func (dc *driverConn) releaseConn(err error) {
-	dc.db.putConn(dc, err, true)
+	dc.db.putConn(dc, err)
 }
 
 func (dc *driverConn) removeOpenStmt(ds *driverStmt) {
@@ -421,19 +417,6 @@ func (dc *driverConn) prepareLocked(ctx context.Context, cg stmtConnGrabber, que
 	return ds, nil
 }
 
-// resetSession resets the connection session and sets the lastErr
-// that is checked before returning the connection to another query.
-//
-// resetSession assumes that the embedded mutex is locked when the connection
-// was returned to the pool. This unlocks the mutex.
-func (dc *driverConn) resetSession(ctx context.Context) {
-	defer dc.Unlock() // In case of panic.
-	if dc.closed {    // Check if the database has been closed.
-		return
-	}
-	dc.lastErr = dc.ci.(driver.ResetSessioner).ResetSession(ctx)
-}
-
 // the dc.db's Mutex is held.
 func (dc *driverConn) closeDBLocked() func() error {
 	dc.Lock()
@@ -621,18 +604,14 @@ func (t dsnConnector) Driver() driver.Driver {
 // function should be called just once. It is rarely necessary to
 // close a DB.
 func OpenDB(c driver.Connector) *DB {
-	ctx, cancel := context.WithCancel(context.Background())
 	db := &DB{
 		connector:    c,
 		openerCh:     make(chan struct{}, connectionRequestQueueSize),
-		resetterCh:   make(chan *driverConn, 50),
 		lastPut:      make(map[*driverConn]string),
 		connRequests: make(map[uint64]chan connRequest),
-		stop:         cancel,
 	}
 
-	go db.connectionOpener(ctx)
-	go db.connectionResetter(ctx)
+	go db.connectionOpener()
 
 	return db
 }
@@ -714,6 +693,7 @@ func (db *DB) Close() error {
 		db.mu.Unlock()
 		return nil
 	}
+	close(db.openerCh)
 	if db.cleanerCh != nil {
 		close(db.cleanerCh)
 	}
@@ -734,7 +714,6 @@ func (db *DB) Close() error {
 			err = err1
 		}
 	}
-	db.stop()
 	return err
 }
 
@@ -922,39 +901,18 @@ func (db *DB) maybeOpenNewConnections() {
 }
 
 // Runs in a separate goroutine, opens new connections when requested.
-func (db *DB) connectionOpener(ctx context.Context) {
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case <-db.openerCh:
-			db.openNewConnection(ctx)
-		}
-	}
-}
-
-// connectionResetter runs in a separate goroutine to reset connections async
-// to exported API.
-func (db *DB) connectionResetter(ctx context.Context) {
-	for {
-		select {
-		case <-ctx.Done():
-			for dc := range db.resetterCh {
-				dc.Unlock()
-			}
-			return
-		case dc := <-db.resetterCh:
-			dc.resetSession(ctx)
-		}
+func (db *DB) connectionOpener() {
+	for range db.openerCh {
+		db.openNewConnection()
 	}
 }
 
 // Open one new connection
-func (db *DB) openNewConnection(ctx context.Context) {
+func (db *DB) openNewConnection() {
 	// maybeOpenNewConnctions has already executed db.numOpen++ before it sent
 	// on db.openerCh. This function must execute db.numOpen-- if the
 	// connection fails or is closed before returning.
-	ci, err := db.connector.Connect(ctx)
+	ci, err := db.connector.Connect(context.Background())
 	db.mu.Lock()
 	defer db.mu.Unlock()
 	if db.closed {
@@ -1029,14 +987,6 @@ func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn
 			conn.Close()
 			return nil, driver.ErrBadConn
 		}
-		// Lock around reading lastErr to ensure the session resetter finished.
-		conn.Lock()
-		err := conn.lastErr
-		conn.Unlock()
-		if err == driver.ErrBadConn {
-			conn.Close()
-			return nil, driver.ErrBadConn
-		}
 		return conn, nil
 	}
 
@@ -1062,7 +1012,7 @@ func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn
 			default:
 			case ret, ok := <-req:
 				if ok {
-					db.putConn(ret.conn, ret.err, false)
+					db.putConn(ret.conn, ret.err)
 				}
 			}
 			return nil, ctx.Err()
@@ -1074,17 +1024,6 @@ func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn
 				ret.conn.Close()
 				return nil, driver.ErrBadConn
 			}
-			if ret.conn == nil {
-				return nil, ret.err
-			}
-			// Lock around reading lastErr to ensure the session resetter finished.
-			ret.conn.Lock()
-			err := ret.conn.lastErr
-			ret.conn.Unlock()
-			if err == driver.ErrBadConn {
-				ret.conn.Close()
-				return nil, driver.ErrBadConn
-			}
 			return ret.conn, ret.err
 		}
 	}
@@ -1140,7 +1079,7 @@ const debugGetPut = false
 
 // putConn adds a connection to the db's free pool.
 // err is optionally the last error that occurred on this connection.
-func (db *DB) putConn(dc *driverConn, err error, resetSession bool) {
+func (db *DB) putConn(dc *driverConn, err error) {
 	db.mu.Lock()
 	if !dc.inUse {
 		if debugGetPut {
@@ -1171,35 +1110,11 @@ func (db *DB) putConn(dc *driverConn, err error, resetSession bool) {
 	if putConnHook != nil {
 		putConnHook(db, dc)
 	}
-	if resetSession {
-		if _, resetSession = dc.ci.(driver.ResetSessioner); resetSession {
-			// Lock the driverConn here so it isn't released until
-			// the connection is reset.
-			// The lock must be taken before the connection is put into
-			// the pool to prevent it from being taken out before it is reset.
-			dc.Lock()
-		}
-	}
 	added := db.putConnDBLocked(dc, nil)
 	db.mu.Unlock()
 
 	if !added {
-		if resetSession {
-			dc.Unlock()
-		}
 		dc.Close()
-		return
-	}
-	if !resetSession {
-		return
-	}
-	select {
-	default:
-		// If the resetterCh is blocking then mark the connection
-		// as bad and continue on.
-		dc.lastErr = driver.ErrBadConn
-		dc.Unlock()
-	case db.resetterCh <- dc:
 	}
 }