cmd/go/internal/work: make NewBuilder safe for concurrent and repeated use

Ever since 'go build' was added (in CL 5483069), it has used an atexit
handler to clean up working directories. At some point (prior to CL
95900044), Init was called multiple times per builder, registering
potentially many atexit handlers that execute asynchronously and make
debugging more difficult.

The use of an AtExit handler also makes the Builder (and anything that
uses it) prone to races: the base.AtExit API is not designed for
concurrent use, but cmd/go is becoming increasingly concurrent over
time. The AtExit handler also makes the Builder inappropriate to use
within a unit-test, since the handlers do not run during the test
function and accumulate over time.

This change makes NewBuilder safe for concurrent use by registering
the AtExit handler only once (during BuildInit, which was already not
safe for concurrent use), and using a sync.Map to store the set of
builders that need cleanup in case of an unclean exit. In addition, it
causes the test variant of cmd/go to fail if any Builder instance
leaks from a clean exit, helping to ensure that functions that create
Builders do not leak them indefinitely, especially in tests.

Updates #54423.

Change-Id: Ia227b15b8fa53c33177c71271d756ac0858feebe
Reviewed-on: https://go-review.googlesource.com/c/go/+/425254
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/cmd/go/script_test.go b/src/cmd/go/script_test.go
index ca76ab5ab8..b2f68b67f9 100644
--- a/src/cmd/go/script_test.go
+++ b/src/cmd/go/script_test.go
@@ -577,6 +577,11 @@ func (ts *testScript) cmdCc(want simpleStatus, args []string) {
 	}
 
 	b := work.NewBuilder(ts.workdir)
+	defer func() {
+		if err := b.Close(); err != nil {
+			ts.fatalf("%v", err)
+		}
+	}()
 	ts.cmdExec(want, append(b.GccCmd(".", ""), args...))
 }