1 files changed, 45 insertions, 0 deletions
diff --git a/src/runtime/debuglog_on.go b/src/runtime/debuglog_on.go
new file mode 100644
index 0000000..3d477e8
--- /dev/null
+++ b/src/runtime/debuglog_on.go
@@ -0,0 +1,45 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build debuglog
+
+package runtime
+
+const dlogEnabled = true
+
+// dlogPerM is the per-M debug log data. This is embedded in the m
+// struct.
+type dlogPerM struct {
+	dlogCache *dlogger
+}
+
+// getCachedDlogger returns a cached dlogger if it can do so
+// efficiently, or nil otherwise. The returned dlogger will be owned.
+func getCachedDlogger() *dlogger {
+	mp := acquirem()
+	// We don't return a cached dlogger if we're running on the
+	// signal stack in case the signal arrived while in
+	// get/putCachedDlogger. (Too bad we don't have non-atomic
+	// exchange!)
+	var l *dlogger
+	if getg() != mp.gsignal {
+		l = mp.dlogCache
+		mp.dlogCache = nil
+	}
+	releasem(mp)
+	return l
+}
+
+// putCachedDlogger attempts to return l to the local cache. It
+// returns false if this fails.
+func putCachedDlogger(l *dlogger) bool {
+	mp := acquirem()
+	if getg() != mp.gsignal && mp.dlogCache == nil {
+		mp.dlogCache = l
+		releasem(mp)
+		return true
+	}
+	releasem(mp)
+	return false
+}