database/sql: use slices rather than container/list

Significantly reduces the number of allocations, while also
simplifying the code and increasing performance by a 1-2%.

benchmark                          old ns/op     new ns/op     delta
BenchmarkConcurrentDBExec          13290567      13026236      -1.99%
BenchmarkConcurrentStmtQuery       13249399      13008879      -1.82%
BenchmarkConcurrentStmtExec        8806237       8680182       -1.43%
BenchmarkConcurrentTxQuery         13628379      12756293      -6.40%
BenchmarkConcurrentTxExec          4794800       4722440       -1.51%
BenchmarkConcurrentTxStmtQuery     5040804       5200721       +3.17%
BenchmarkConcurrentTxStmtExec      1366574       1336626       -2.19%
BenchmarkConcurrentRandom          11119120      10926113      -1.74%

benchmark                          old allocs     new allocs     delta
BenchmarkConcurrentDBExec          14191          13684          -3.57%
BenchmarkConcurrentStmtQuery       16020          15514          -3.16%
BenchmarkConcurrentStmtExec        4179           3672           -12.13%
BenchmarkConcurrentTxQuery         16025          15518          -3.16%
BenchmarkConcurrentTxExec          12717          12709          -0.06%
BenchmarkConcurrentTxStmtQuery     15532          15525          -0.05%
BenchmarkConcurrentTxStmtExec      2175           2168           -0.32%
BenchmarkConcurrentRandom          12320          11997          -2.62%

benchmark                          old bytes     new bytes     delta
BenchmarkConcurrentDBExec          2164827       2139760       -1.16%
BenchmarkConcurrentStmtQuery       2418070       2394030       -0.99%
BenchmarkConcurrentStmtExec        1728782       1704371       -1.41%
BenchmarkConcurrentTxQuery         2477144       2452620       -0.99%
BenchmarkConcurrentTxExec          588920        588343        -0.10%
BenchmarkConcurrentTxStmtQuery     790866        796578        +0.72%
BenchmarkConcurrentTxStmtExec      98502         98143         -0.36%
BenchmarkConcurrentRandom          1725906       1710220       -0.91%

LGTM=ruiu, dave, bradfitz
R=golang-codereviews, ruiu, gobot, bradfitz, dave, minux
CC=bradfitz, golang-codereviews
https://golang.org/cl/107020044

1 files changed, 21 insertions, 15 deletions

diff --git a/src/pkg/database/sql/sql_test.go b/src/pkg/database/sql/sql_test.go
index 71c81d6f76..8849c81c4b 100644
--- a/src/pkg/database/sql/sql_test.go
+++ b/src/pkg/database/sql/sql_test.go
@@ -24,7 +24,14 @@ func init() {
 	}
 	freedFrom := make(map[dbConn]string)
 	putConnHook = func(db *DB, c *driverConn) {
-		if c.listElem != nil {
+		idx := -1
+		for i, v := range db.freeConn {
+			if v == c {
+				idx = i
+				break
+			}
+		}
+		if idx >= 0 {
 			// print before panic, as panic may get lost due to conflicting panic
 			// (all goroutines asleep) elsewhere, since we might not unlock
 			// the mutex in freeConn here.
@@ -79,15 +86,14 @@ func closeDB(t testing.TB, db *DB) {
 			t.Errorf("Error closing fakeConn: %v", err)
 		}
 	})
-	for node, i := db.freeConn.Front(), 0; node != nil; node, i = node.Next(), i+1 {
-		dc := node.Value.(*driverConn)
+	for i, dc := range db.freeConn {
 		if n := len(dc.openStmt); n > 0 {
 			// Just a sanity check. This is legal in
 			// general, but if we make the tests clean up
 			// their statements first, then we can safely
 			// verify this is always zero here, and any
 			// other value is a leak.
-			t.Errorf("while closing db, freeConn %d/%d had %d open stmts; want 0", i, db.freeConn.Len(), n)
+			t.Errorf("while closing db, freeConn %d/%d had %d open stmts; want 0", i, len(db.freeConn), n)
 		}
 	}
 	err := db.Close()
@@ -105,10 +111,10 @@ func closeDB(t testing.TB, db *DB) {
 // numPrepares assumes that db has exactly 1 idle conn and returns
 // its count of calls to Prepare
 func numPrepares(t *testing.T, db *DB) int {
-	if n := db.freeConn.Len(); n != 1 {
+	if n := len(db.freeConn); n != 1 {
 		t.Fatalf("free conns = %d; want 1", n)
 	}
-	return (db.freeConn.Front().Value.(*driverConn)).ci.(*fakeConn).numPrepare
+	return db.freeConn[0].ci.(*fakeConn).numPrepare
 }
 
 func (db *DB) numDeps() int {
@@ -133,7 +139,7 @@ func (db *DB) numDepsPollUntil(want int, d time.Duration) int {
 func (db *DB) numFreeConns() int {
 	db.mu.Lock()
 	defer db.mu.Unlock()
-	return db.freeConn.Len()
+	return len(db.freeConn)
 }
 
 func (db *DB) dumpDeps(t *testing.T) {
@@ -650,10 +656,10 @@ func TestQueryRowClosingStmt(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if db.freeConn.Len() != 1 {
+	if len(db.freeConn) != 1 {
 		t.Fatalf("expected 1 free conn")
 	}
-	fakeConn := (db.freeConn.Front().Value.(*driverConn)).ci.(*fakeConn)
+	fakeConn := db.freeConn[0].ci.(*fakeConn)
 	if made, closed := fakeConn.stmtsMade, fakeConn.stmtsClosed; made != closed {
 		t.Errorf("statement close mismatch: made %d, closed %d", made, closed)
 	}
@@ -878,13 +884,13 @@ func TestMaxIdleConns(t *testing.T) {
 		t.Fatal(err)
 	}
 	tx.Commit()
-	if got := db.freeConn.Len(); got != 1 {
+	if got := len(db.freeConn); got != 1 {
 		t.Errorf("freeConns = %d; want 1", got)
 	}
 
 	db.SetMaxIdleConns(0)
 
-	if got := db.freeConn.Len(); got != 0 {
+	if got := len(db.freeConn); got != 0 {
 		t.Errorf("freeConns after set to zero = %d; want 0", got)
 	}
 
@@ -893,7 +899,7 @@ func TestMaxIdleConns(t *testing.T) {
 		t.Fatal(err)
 	}
 	tx.Commit()
-	if got := db.freeConn.Len(); got != 0 {
+	if got := len(db.freeConn); got != 0 {
 		t.Errorf("freeConns = %d; want 0", got)
 	}
 }
@@ -1180,10 +1186,10 @@ func TestCloseConnBeforeStmts(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if db.freeConn.Len() != 1 {
-		t.Fatalf("expected 1 freeConn; got %d", db.freeConn.Len())
+	if len(db.freeConn) != 1 {
+		t.Fatalf("expected 1 freeConn; got %d", len(db.freeConn))
 	}
-	dc := db.freeConn.Front().Value.(*driverConn)
+	dc := db.freeConn[0]
 	if dc.closed {
 		t.Errorf("conn shouldn't be closed")
 	}