Merge branch 'fix-ConcurrentReadableArray-double-free' into fix-metadatalookup-deadlocks

Author: mikeash

benchmark/single-source/StringBuilder.swift

@@ -21,6 +21,10 @@ public let StringBuilder = [
     name: "StringBuilder",
     runFunction: run_StringBuilder,
     tags: [.validation, .api, .String]),
+  BenchmarkInfo(
+    name: "StringBuilderSmallReservingCapacity",
+    runFunction: run_StringBuilderSmallReservingCapacity,
+    tags: [.validation, .api, .String]),
   BenchmarkInfo(
     name: "StringUTF16Builder",
     runFunction: run_StringUTF16Builder,
@@ -48,8 +52,11 @@ public let StringBuilder = [
 ]
 
 @inline(never)
-func buildString(_ i: String) -> String {
+func buildString(_ i: String, reservingCapacity: Bool = false) -> String {
   var sb = getString(i)
+  if reservingCapacity {
+    sb.reserveCapacity(10)
+  }
   for str in ["b","c","d","pizza"] {
     sb += str
   }
@@ -63,6 +70,13 @@ public func run_StringBuilder(_ N: Int) {
   }
 }
 
+@inline(never)
+public func run_StringBuilderSmallReservingCapacity(_ N: Int) {
+  for _ in 1...5000*N {
+    blackHole(buildString("a", reservingCapacity: true))
+  }
+}
+
 @inline(never)
 func addString(_ i: String) -> String {
   let s = getString(i) + "b" + "c" + "d" + "pizza"
@@ -179,3 +193,4 @@ public func run_StringWordBuilderReservingCapacity(_ N: Int) {
   blackHole(buildString(
     word: "bumfuzzle", count: 50_000 * N, reservingCapacity: true))
 }
+