database/sql: deflake TestPendingConnsAfterErr and fix races, panics

TestPendingConnsAfterErr only cared that things didn't deadlock, so 5
seconds is a sufficient timer. We don't need 100 milliseconds.

I was able to reproduce with a tiny (5 nanosecond) timeout value,
instead of 100 milliseconds. In the process of testing with -race and
a high -count= value, I noticed several data races and panics
(sendings on a closed channel) which are also fixed in this change.

Fixes #15684

Change-Id: Ib4605fcc0f296e658cb948352ed642b801cb578c
Reviewed-on: https://go-review.googlesource.com/24550
Reviewed-by: Marko Tiikkaja <marko@joh.to>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index e7482a8e2f..09de1c34e8 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -718,6 +718,9 @@ func (db *DB) maybeOpenNewConnections() {
 	for numRequests > 0 {
 		db.numOpen++ // optimistically
 		numRequests--
+		if db.closed {
+			return
+		}
 		db.openerCh <- struct{}{}
 	}
 }
@@ -915,6 +918,9 @@ func (db *DB) putConn(dc *driverConn, err error) {
 // If a connRequest was fulfilled or the *driverConn was placed in the
 // freeConn list, then true is returned, otherwise false is returned.
 func (db *DB) putConnDBLocked(dc *driverConn, err error) bool {
+	if db.closed {
+		return false
+	}
 	if db.maxOpen > 0 && db.numOpen > db.maxOpen {
 		return false
 	}