Bug 1874226 - DebugFilesAutoLock to lock/unlock in ctor/dtor instead …

…of via Scoped<> inheritance. r=xpcom-reviewers,emilio

Differential Revision: https://phabricator.services.mozilla.com/D200249

xpcom/build/PoisonIOInterposerBase.cpp

@@ -6,7 +6,6 @@
 
 #include "mozilla/Maybe.h"
 #include "mozilla/Mutex.h"
-#include "mozilla/Scoped.h"
 #include "mozilla/UniquePtr.h"
 
 #include <algorithm>
@@ -38,40 +37,17 @@ inline mozilla::Maybe<intptr_t> FileDescriptorToHandle(int aFd) {
 
 namespace {
 
-struct DebugFilesAutoLockTraits {
-  typedef PRLock* type;
-  typedef const PRLock* const_type;
-  static const_type empty() { return nullptr; }
-  static void release(type aL) { PR_Unlock(aL); }
-};
-
-class DebugFilesAutoLock : public mozilla::Scoped<DebugFilesAutoLockTraits> {
-  static PRLock* Lock;
-
+class DebugFilesAutoLock final {
  public:
   static PRLock* getDebugFileIDsLock() {
-    // On windows this static is not thread safe, but we know that the first
-    // call is from
-    // * An early registration of a debug FD or
-    // * The call to InitWritePoisoning.
-    // Since the early debug FDs are logs created early in the main thread
-    // and no writes are trapped before InitWritePoisoning, we are safe.
-    if (!Lock) {
-      Lock = PR_NewLock();
-    }
-
-    // We have to use something lower level than a mutex. If we don't, we
-    // can get recursive in here when called from logging a call to free.
-    return Lock;
+    static PRLock* sLock = PR_NewLock();
+    return sLock;
   }
 
-  DebugFilesAutoLock()
-      : mozilla::Scoped<DebugFilesAutoLockTraits>(getDebugFileIDsLock()) {
-    PR_Lock(get());
-  }
-};
+  DebugFilesAutoLock() { PR_Lock(getDebugFileIDsLock()); }
 
-PRLock* DebugFilesAutoLock::Lock;
+  ~DebugFilesAutoLock() { PR_Unlock(getDebugFileIDsLock()); }
+};
 
 // The ChunkedList<T> class implements, at the high level, a non-iterable
 // list of instances of T. Its goal is to be somehow minimalist for the