runtime: remove -tags=threadprof in tests

Use an enviroment variable rather than a build tag to control starting
a busy loop thread when testprogcgo starts. This lets us skip another
build that invokes the C compiler and linker, which should avoid
timeouts running the runtime tests.

Fixes #44422

Change-Id: I516668d71a373da311d844990236566ff63e6d72
Reviewed-on: https://go-review.googlesource.com/c/go/+/379294
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 12 insertions, 7 deletions

diff --git a/src/runtime/testdata/testprogcgo/threadprof.go b/src/runtime/testdata/testprogcgo/threadprof.go
index 8081173c0f..d62d4b4be8 100644
--- a/src/runtime/testdata/testprogcgo/threadprof.go
+++ b/src/runtime/testdata/testprogcgo/threadprof.go
@@ -2,21 +2,22 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// We only build this file with the tag "threadprof", since it starts
-// a thread running a busy loop at constructor time.
-
-//go:build !plan9 && !windows && threadprof
-// +build !plan9,!windows,threadprof
+//go:build !plan9 && !windows
+// +build !plan9,!windows
 
 package main
 
 /*
 #include <stdint.h>
+#include <stdlib.h>
 #include <signal.h>
 #include <pthread.h>
 
 volatile int32_t spinlock;
 
+// Note that this thread is only started if GO_START_SIGPROF_THREAD
+// is set in the environment, which is only done when running the
+// CgoExternalThreadSIGPROF test.
 static void *thread1(void *p) {
 	(void)p;
 	while (spinlock == 0)
@@ -26,9 +27,13 @@ static void *thread1(void *p) {
 	return NULL;
 }
 
+// This constructor function is run when the program starts.
+// It is used for the CgoExternalThreadSIGPROF test.
 __attribute__((constructor)) void issue9456() {
-	pthread_t tid;
-	pthread_create(&tid, 0, thread1, NULL);
+	if (getenv("GO_START_SIGPROF_THREAD") != NULL) {
+		pthread_t tid;
+		pthread_create(&tid, 0, thread1, NULL);
+	}
 }
 
 void **nullptr;