1 files changed, 175 insertions, 0 deletions
diff --git a/gfx/2d/IterableArena.h b/gfx/2d/IterableArena.h
new file mode 100644
index 0000000000..6f90e7d603
--- /dev/null
+++ b/gfx/2d/IterableArena.h
@@ -0,0 +1,175 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 MOZILLA_GFX_ITERABLEARENA_H_
+#define MOZILLA_GFX_ITERABLEARENA_H_
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <utility>
+#include <vector>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/gfx/Logging.h"
+
+namespace mozilla {
+namespace gfx {
+
+/// A simple pool allocator for plain data structures.
+///
+/// Beware that the pool will not attempt to run the destructors. It is the
+/// responsibility of the user of this class to either use objects with no
+/// destructor or to manually call the allocated objects destructors.
+/// If the pool is growable, its allocated objects must be safely moveable in
+/// in memory (through memcpy).
+class IterableArena {
+ protected:
+  struct Header {
+    size_t mBlocSize;
+  };
+
+ public:
+  enum ArenaType { FIXED_SIZE, GROWABLE };
+
+  IterableArena(ArenaType aType, size_t aStorageSize)
+      : mSize(aStorageSize), mCursor(0), mIsGrowable(aType == GROWABLE) {
+    if (mSize == 0) {
+      mSize = 128;
+    }
+
+    mStorage = (uint8_t*)malloc(mSize);
+    if (mStorage == nullptr) {
+      gfxCriticalError() << "Not enough Memory allocate a memory pool of size "
+                         << aStorageSize;
+      MOZ_CRASH("GFX: Out of memory IterableArena");
+    }
+  }
+
+  ~IterableArena() { free(mStorage); }
+
+  /// Constructs a new item in the pool and returns a positive offset in case of
+  /// success.
+  ///
+  /// The offset never changes even if the storage is reallocated, so users
+  /// of this class should prefer storing offsets rather than direct pointers
+  /// to the allocated objects.
+  /// Alloc can cause the storage to be reallocated if the pool was initialized
+  /// with IterableArena::GROWABLE.
+  /// If for any reason the pool fails to allocate enough space for the new item
+  /// Alloc returns a negative offset and the object's constructor is not
+  /// called.
+  template <typename T, typename... Args>
+  ptrdiff_t Alloc(Args&&... aArgs) {
+    void* storage = nullptr;
+    auto offset = AllocRaw(sizeof(T), &storage);
+    if (offset < 0) {
+      return offset;
+    }
+    new (storage) T(std::forward<Args>(aArgs)...);
+    return offset;
+  }
+
+  ptrdiff_t AllocRaw(size_t aSize, void** aOutPtr = nullptr) {
+    const size_t blocSize = AlignedSize(sizeof(Header) + aSize);
+
+    if (AlignedSize(mCursor + blocSize) > mSize) {
+      if (!mIsGrowable) {
+        return -1;
+      }
+
+      size_t newSize = mSize * 2;
+      while (AlignedSize(mCursor + blocSize) > newSize) {
+        newSize *= 2;
+      }
+
+      uint8_t* newStorage = (uint8_t*)realloc(mStorage, newSize);
+      if (!newStorage) {
+        gfxCriticalError()
+            << "Not enough Memory to grow the memory pool, size: " << newSize;
+        return -1;
+      }
+
+      mStorage = newStorage;
+      mSize = newSize;
+    }
+    ptrdiff_t offset = mCursor;
+    GetHeader(offset)->mBlocSize = blocSize;
+    mCursor += blocSize;
+    if (aOutPtr) {
+      *aOutPtr = GetStorage(offset);
+    }
+    return offset;
+  }
+
+  /// Get access to an allocated item at a given offset (only use offsets
+  /// returned by Alloc or AllocRaw).
+  ///
+  /// If the pool is growable, the returned pointer is only valid temporarily.
+  /// The underlying storage can be reallocated in Alloc or AllocRaw, so do not
+  /// keep these pointers around and store the offset instead.
+  void* GetStorage(ptrdiff_t offset = 0) {
+    MOZ_ASSERT(offset >= 0);
+    MOZ_ASSERT(offset < mCursor);
+    return offset >= 0 ? mStorage + offset + sizeof(Header) : nullptr;
+  }
+
+  /// Clears the storage without running any destructor and without deallocating
+  /// it.
+  void Clear() { mCursor = 0; }
+
+  /// Iterate over the elements allocated in this pool.
+  ///
+  /// Takes a lambda or function object accepting a void* as parameter.
+  template <typename Func>
+  void ForEach(Func cb) {
+    Iterator it;
+    while (void* ptr = it.Next(this)) {
+      cb(ptr);
+    }
+  }
+
+  /// A simple iterator over an arena.
+  class Iterator {
+   public:
+    Iterator() : mCursor(0) {}
+
+    void* Next(IterableArena* aArena) {
+      if (mCursor >= aArena->mCursor) {
+        return nullptr;
+      }
+      void* result = aArena->GetStorage(mCursor);
+      const size_t blocSize = aArena->GetHeader(mCursor)->mBlocSize;
+      MOZ_ASSERT(blocSize != 0);
+      mCursor += blocSize;
+      return result;
+    }
+
+   private:
+    ptrdiff_t mCursor;
+  };
+
+ protected:
+  Header* GetHeader(ptrdiff_t offset) { return (Header*)(mStorage + offset); }
+
+  size_t AlignedSize(size_t aSize) const {
+    const size_t alignment = sizeof(uintptr_t);
+    return aSize + (alignment - (aSize % alignment)) % alignment;
+  }
+
+  uint8_t* mStorage;
+  uint32_t mSize;
+  ptrdiff_t mCursor;
+  bool mIsGrowable;
+
+  friend class Iterator;
+};
+
+}  // namespace gfx
+}  // namespace mozilla
+
+#endif