Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 184 insertions, 0 deletions

diff --git a/xpcom/string/nsStringBuffer.h b/xpcom/string/nsStringBuffer.h
new file mode 100644
index 0000000000..3c92959932
--- /dev/null
+++ b/xpcom/string/nsStringBuffer.h
@@ -0,0 +1,184 @@
+/* -*- 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 nsStringBuffer_h__
+#define nsStringBuffer_h__
+
+#include <atomic>
+#include "mozilla/MemoryReporting.h"
+#include "nsStringFwd.h"
+
+template <class T>
+struct already_AddRefed;
+
+/**
+ * This structure precedes the string buffers "we" allocate.  It may be the
+ * case that nsTAString::mData does not point to one of these special
+ * buffers.  The mDataFlags member variable distinguishes the buffer type.
+ *
+ * When this header is in use, it enables reference counting, and capacity
+ * tracking.  NOTE: A string buffer can be modified only if its reference
+ * count is 1.
+ */
+class nsStringBuffer {
+ private:
+  friend class CheckStaticAtomSizes;
+
+  std::atomic<uint32_t> mRefCount;
+  uint32_t mStorageSize;
+
+ public:
+  /**
+   * Allocates a new string buffer, with given size in bytes and a
+   * reference count of one.  When the string buffer is no longer needed,
+   * it should be released via Release.
+   *
+   * It is up to the caller to set the bytes corresponding to the string
+   * buffer by calling the Data method to fetch the raw data pointer.  Care
+   * must be taken to properly null terminate the character array.  The
+   * storage size can be greater than the length of the actual string
+   * (i.e., it is not required that the null terminator appear in the last
+   * storage unit of the string buffer's data).
+   *
+   * @return new string buffer or null if out of memory.
+   */
+  static already_AddRefed<nsStringBuffer> Alloc(size_t aStorageSize);
+
+  /**
+   * Resizes the given string buffer to the specified storage size.  This
+   * method must not be called on a readonly string buffer.  Use this API
+   * carefully!!
+   *
+   * This method behaves like the ANSI-C realloc function.  (i.e., If the
+   * allocation fails, null will be returned and the given string buffer
+   * will remain unmodified.)
+   *
+   * @see IsReadonly
+   */
+  static nsStringBuffer* Realloc(nsStringBuffer* aBuf, size_t aStorageSize);
+
+  /**
+   * Increment the reference count on this string buffer.
+   */
+  void NS_FASTCALL AddRef();
+
+  /**
+   * Decrement the reference count on this string buffer.  The string
+   * buffer will be destroyed when its reference count reaches zero.
+   */
+  void NS_FASTCALL Release();
+
+  /**
+   * This method returns the string buffer corresponding to the given data
+   * pointer.  The data pointer must have been returned previously by a
+   * call to the nsStringBuffer::Data method.
+   */
+  static nsStringBuffer* FromData(void* aData) {
+    return reinterpret_cast<nsStringBuffer*>(aData) - 1;
+  }
+
+  /**
+   * This method returns the data pointer for this string buffer.
+   */
+  void* Data() const {
+    return const_cast<char*>(reinterpret_cast<const char*>(this + 1));
+  }
+
+  /**
+   * This function returns the storage size of a string buffer in bytes.
+   * This value is the same value that was originally passed to Alloc (or
+   * Realloc).
+   */
+  uint32_t StorageSize() const { return mStorageSize; }
+
+  /**
+   * If this method returns false, then the caller can be sure that their
+   * reference to the string buffer is the only reference to the string
+   * buffer, and therefore it has exclusive access to the string buffer and
+   * associated data.  However, if this function returns true, then other
+   * consumers may rely on the data in this buffer being immutable and
+   * other threads may access this buffer simultaneously.
+   */
+  bool IsReadonly() const {
+    // This doesn't lead to the destruction of the buffer, so we don't
+    // need to perform acquire memory synchronization for the normal
+    // reason that a reference count needs acquire synchronization
+    // (ensuring that all writes to the object made on other threads are
+    // visible to the thread destroying the object).
+    //
+    // We then need to consider the possibility that there were prior
+    // writes to the buffer on a different thread:  one that has either
+    // since released its reference count, or one that also has access
+    // to this buffer through the same reference.  There are two ways
+    // for that to happen: either the buffer pointer or a data structure
+    // (e.g., string object) pointing to the buffer was transferred from
+    // one thread to another, or the data structure pointing to the
+    // buffer was already visible on both threads.  In the first case
+    // (transfer), the transfer of data from one thread to another would
+    // have handled the memory synchronization.  In the latter case
+    // (data structure visible on both threads), the caller needed some
+    // sort of higher level memory synchronization to protect against
+    // the string object being mutated at the same time on multiple
+    // threads.
+
+    // See bug 1603504. TSan might complain about a race when using
+    // memory_order_relaxed, so use memory_order_acquire for making TSan
+    // happy.
+#if defined(MOZ_TSAN)
+    return mRefCount.load(std::memory_order_acquire) > 1;
+#else
+    return mRefCount.load(std::memory_order_relaxed) > 1;
+#endif
+  }
+
+  /**
+   * The FromString methods return a string buffer for the given string
+   * object or null if the string object does not have a string buffer.
+   * The reference count of the string buffer is NOT incremented by these
+   * methods.  If the caller wishes to hold onto the returned value, then
+   * the returned string buffer must have its reference count incremented
+   * via a call to the AddRef method.
+   */
+  static nsStringBuffer* FromString(const nsAString& aStr);
+  static nsStringBuffer* FromString(const nsACString& aStr);
+
+  /**
+   * The ToString methods assign this string buffer to a given string
+   * object.  If the string object does not support sharable string
+   * buffers, then its value will be set to a copy of the given string
+   * buffer.  Otherwise, these methods increment the reference count of the
+   * given string buffer.  It is important to specify the length (in
+   * storage units) of the string contained in the string buffer since the
+   * length of the string may be less than its storage size.  The string
+   * must have a null terminator at the offset specified by |len|.
+   *
+   * NOTE: storage size is measured in bytes even for wide strings;
+   *       however, string length is always measured in storage units
+   *       (2-byte units for wide strings).
+   */
+  void ToString(uint32_t aLen, nsAString& aStr, bool aMoveOwnership = false);
+  void ToString(uint32_t aLen, nsACString& aStr, bool aMoveOwnership = false);
+
+  /**
+   * This measures the size only if the StringBuffer is unshared.
+   */
+  size_t SizeOfIncludingThisIfUnshared(
+      mozilla::MallocSizeOf aMallocSizeOf) const;
+
+  /**
+   * This measures the size regardless of whether the StringBuffer is
+   * unshared.
+   *
+   * WARNING: Only use this if you really know what you are doing, because
+   * it can easily lead to double-counting strings.  If you do use them,
+   * please explain clearly in a comment why it's safe and won't lead to
+   * double-counting.
+   */
+  size_t SizeOfIncludingThisEvenIfShared(
+      mozilla::MallocSizeOf aMallocSizeOf) const;
+};
+
+#endif /* !defined(nsStringBuffer_h__ */