refactor

src/runtime/gc_custom_extalloc.go

@@ -59,7 +59,8 @@ var (
 // of all allocations and to find references between them.
 type allocEntry struct {
 	start, end uintptr // header + data + padding
-	next       *allocEntry
+	marked     bool
+	next       *allocEntry // used by the scan queue
 }
 
 // Representation of a slice header (without the backing array).
@@ -417,18 +418,11 @@ func mark(addr uintptr) bool {
 
 	// Search the allocation list for the address and mark it if found
 	curAlloc := searchAllocations(addr)
-
-	if curAlloc != nil && curAlloc.next == nil {
+	if curAlloc != nil && !curAlloc.marked {
+		curAlloc.marked = true
 		// Push the allocation onto the scan queue
-		nextAlloc := scanQueue
-
-		if nextAlloc == nil {
-			// Insert a loop, so we can tell that this isn't marked
-			nextAlloc = curAlloc
-		}
-
-		scanQueue, curAlloc.next = curAlloc, nextAlloc
-
+		curAlloc.next = scanQueue
+		scanQueue = curAlloc
 		return true
 	}
 
@@ -443,15 +437,7 @@ func finishMarking() {
 	for scanQueue != nil {
 		// Pop a marked allocation off of the scan queue.
 		curAlloc := scanQueue
-		nextAlloc := curAlloc.next
-
-		// This is the last value on the queue.
-		if nextAlloc == curAlloc {
-			nextAlloc = nil
-		}
-
-		scanQueue = nextAlloc
-
+		scanQueue = curAlloc.next
 		// Scan and mark all allocations that are referenced
 		// by this allocation and adds them to the scan queue.
 		scan(curAlloc.start, curAlloc.end)
@@ -465,25 +451,23 @@ func sweep() {
 
 	for _, curAlloc := range allocations {
 		// This was never marked
-		if curAlloc.next == nil {
+		if !curAlloc.marked {
 			free(unsafe.Pointer(curAlloc.start))
 			continue
 		}
-		// Move this down in the list
+		// Move this down in the list to keep it compact
 		allocations[j] = curAlloc
 		j++
-
-		// Re-calculate used memory.
 		gcTotalAlloc += uint64(curAlloc.end - curAlloc.start)
 	}
 
-	// Remove the allocation from the list of allocations
 	allocations = allocations[:j]
 }
 
 // Unmarks all allocations in the allocations list.
 func unmarkAllocations() {
 	for i := range allocations {
+		allocations[i].marked = false
 		allocations[i].next = nil
 	}
 }