[runtime] Add support for an asserts only debugging routine called swift_dumpTrackedAccesses().

This makes it easy to perform printf debugging in the debugger. I have found it
to be useful in understanding programs around exclusivity quickly.

Author: gottesmm

include/swift/Runtime/Exclusivity.h

@@ -58,6 +58,19 @@ void swift_endAccess(ValueBuffer *buffer);
 SWIFT_RUNTIME_EXPORT
 bool _swift_disableExclusivityChecking;
 
+#ifndef NDEBUG
+
+/// Dump all accesses currently tracked by the runtime.
+///
+/// This is a debug routine that is intended to be used from the debugger and is
+/// compiled out when asserts are disabled. The intention is that it allows one
+/// to dump the access state to easily see if/when exclusivity violations will
+/// happen. This eases debugging.
+SWIFT_RUNTIME_EXPORT
+void swift_dumpTrackedAccesses();
+
+#endif
+
 } // end namespace swift
 
 #endif

stdlib/public/runtime/Exclusivity.cpp

@@ -260,6 +260,16 @@ class AccessSet {
 
     swift_runtime_unreachable("access not found in set");
   }
+
+#ifndef NDEBUG
+  /// Only available with asserts. Intended to be used with
+  /// swift_dumpTrackedAccess().
+  void forEach(std::function<void (Access *)> action) {
+    for (auto *iter = Head; iter != nullptr; iter = iter->getNext()) {
+      action(iter);
+    }
+  }
+#endif
 };
 
 } // end anonymous namespace
@@ -348,3 +358,17 @@ void swift::swift_endAccess(ValueBuffer *buffer) {
 
   getAccessSet().remove(access);
 }
+
+#ifndef NDEBUG
+
+// Dump the accesses that are currently being tracked by the runtime.
+//
+// This is only intended to be used in the debugger.
+void swift::swift_dumpTrackedAccesses() {
+  getAccessSet().forEach([](Access *a) {
+      fprintf(stderr, "Access. Pointer: %p. PC: %p. AccessAction: %s",
+              a->Pointer, a->PC, getAccessName(a->getAccessAction()));
+  });
+}
+
+#endif