import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

layout/base/StackArena.h

@@ -0,0 +1,94 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef StackArena_h
+#define StackArena_h
+
+#include "nsError.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/MemoryReporting.h"
+
+namespace mozilla {
+
+struct StackBlock;
+struct StackMark;
+class AutoStackArena;
+
+// Private helper class for AutoStackArena.
+class StackArena {
+private:
+  friend class AutoStackArena;
+  StackArena();
+  ~StackArena();
+
+  // Memory management functions.
+  void* Allocate(size_t aSize);
+  void Push();
+  void Pop();
+
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+  // Our current position in memory.
+  size_t mPos;
+
+  // A list of memory blocks. Usually there is only one
+  // but if we overrun our stack size we can get more memory.
+  StackBlock* mBlocks;
+
+  // The current block.
+  StackBlock* mCurBlock;
+
+  // Our stack of mark where push has been called.
+  StackMark* mMarks;
+
+  // The current top of the mark list.
+  uint32_t mStackTop;
+
+  // The size of the mark array.
+  uint32_t mMarkLength;
+};
+
+// Class for stack scoped arena memory allocations.
+//
+// Callers who wish to allocate memory whose lifetime corresponds to the
+// lifetime of a stack-allocated object can use this class.  First,
+// declare an AutoStackArena object on the stack.  Then all subsequent
+// calls to Allocate will allocate memory from an arena pool that will
+// be freed when that variable goes out of scope.  Nesting is allowed.
+//
+// Individual allocations cannot exceed StackBlock::MAX_USABLE_SIZE
+// bytes.
+//
+class MOZ_RAII AutoStackArena {
+public:
+  AutoStackArena()
+    : mOwnsStackArena(false)
+  {
+    if (!gStackArena) {
+      gStackArena = new StackArena();
+      mOwnsStackArena = true;
+    }
+    gStackArena->Push();
+  }
+
+  ~AutoStackArena() {
+    gStackArena->Pop();
+    if (mOwnsStackArena) {
+      delete gStackArena;
+      gStackArena = nullptr;
+    }
+  }
+
+  static void* Allocate(size_t aSize) {
+    return gStackArena->Allocate(aSize);
+  }
+
+private:
+  static StackArena* gStackArena;
+  bool mOwnsStackArena;
+};
+
+} // namespace mozilla
+
+#endif