unique: add unique package and implement Make/Handle

This change adds the unique package for canonicalizing values, as
described by the proposal in #62483.

Fixes #62483.

Change-Id: I1dc3d34ec12351cb4dc3838a8ea29a5368d59e99
Reviewed-on: https://go-review.googlesource.com/c/go/+/574355
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ingo Oeser <nightlyone@googlemail.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 3d3ecb0f88..83afd55c47 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -1694,7 +1694,8 @@ func gcResetMarkState() {
 // Hooks for other packages
 
 var poolcleanup func()
-var boringCaches []unsafe.Pointer // for crypto/internal/boring
+var boringCaches []unsafe.Pointer  // for crypto/internal/boring
+var uniqueMapCleanup chan struct{} // for unique
 
 //go:linkname sync_runtime_registerPoolCleanup sync.runtime_registerPoolCleanup
 func sync_runtime_registerPoolCleanup(f func()) {
@@ -1706,6 +1707,18 @@ func boring_registerCache(p unsafe.Pointer) {
 	boringCaches = append(boringCaches, p)
 }
 
+//go:linkname unique_runtime_registerUniqueMapCleanup unique.runtime_registerUniqueMapCleanup
+func unique_runtime_registerUniqueMapCleanup(f func()) {
+	// Start the goroutine in the runtime so it's counted as a system goroutine.
+	uniqueMapCleanup = make(chan struct{}, 1)
+	go func(cleanup func()) {
+		for {
+			<-uniqueMapCleanup
+			cleanup()
+		}
+	}(f)
+}
+
 func clearpools() {
 	// clear sync.Pools
 	if poolcleanup != nil {
@@ -1717,6 +1730,14 @@ func clearpools() {
 		atomicstorep(p, nil)
 	}
 
+	// clear unique maps
+	if uniqueMapCleanup != nil {
+		select {
+		case uniqueMapCleanup <- struct{}{}:
+		default:
+		}
+	}
+
 	// Clear central sudog cache.
 	// Leave per-P caches alone, they have strictly bounded size.
 	// Disconnect cached list before dropping it on the floor,