database/sql: use a value type instead of a pointer

Follow-up to https://golang.org/cl/107020044/
Also add a little comment.

LGTM=ruiu, josharian
R=josharian, ruiu
CC=golang-codereviews
https://golang.org/cl/139760043

diff --git a/src/pkg/database/sql/sql.go b/src/pkg/database/sql/sql.go
index 09f75b647ad60eff950cdcff1d13dd2cbceee98d..63c6dd68167bd48ce5a723b939c5be26e5cc3bdb 100644 (file)
--- a/src/pkg/database/sql/sql.go
+++ b/src/pkg/database/sql/sql.go
@@ -198,7 +198,7 @@ type DB struct {
 
        mu           sync.Mutex // protects following fields
        freeConn     []*driverConn
-       connRequests []chan *connRequest
+       connRequests []chan connRequest
        numOpen      int
        pendingOpens int
        // Used to signal the need for new connections
@@ -626,14 +626,11 @@ func (db *DB) conn() (*driverConn, error) {
        if db.maxOpen > 0 && db.numOpen >= db.maxOpen && len(db.freeConn) == 0 {
                // Make the connRequest channel. It's buffered so that the
                // connectionOpener doesn't block while waiting for the req to be read.
-               req := make(chan *connRequest, 1)
+               req := make(chan connRequest, 1)
                db.connRequests = append(db.connRequests, req)
                db.maybeOpenNewConnections()
                db.mu.Unlock()
                ret := <-req
-               if ret == nil {
-                       return nil, errDBClosed
-               }
                return ret.conn, ret.err
        }
 
@@ -786,12 +783,15 @@ func (db *DB) putConn(dc *driverConn, err error) {
 func (db *DB) putConnDBLocked(dc *driverConn, err error) bool {
        if c := len(db.connRequests); c > 0 {
                req := db.connRequests[0]
+               // This copy is O(n) but in practice faster than a linked list.
+               // TODO: consider compacting it down less often and
+               // moving the base instead?
                copy(db.connRequests, db.connRequests[1:])
                db.connRequests = db.connRequests[:c-1]
                if err == nil {
                        dc.inUse = true
                }
-               req <- &connRequest{
+               req <- connRequest{
                        conn: dc,
                        err:  err,
                }