dom/streams/QueueWithSizes.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_dom_QueueWithSizes_h
   8 #define mozilla_dom_QueueWithSizes_h
   9
  10 #include <cmath>
  11 #include "js/TypeDecls.h"
  12 #include "js/Value.h"
  13 #include "mozilla/ErrorResult.h"
  14 #include "mozilla/UniquePtr.h"
  15 #include "nsTArray.h"
  16
  17 namespace mozilla::dom {
  18
  19 // Note: Consumers of QueueWithSize need to ensure it is traced. See
  20 // ReadableStreamDefaultController.cpp for an example.
  21
  22 struct ValueWithSize : LinkedListElement<ValueWithSize> {
  23   ValueWithSize(JS::Handle<JS::Value> aValue, double aSize)
  24       : mValue(aValue), mSize(aSize){};
  25
  26   JS::Heap<JS::Value> mValue;
  27   double mSize = 0.0f;
  28 };
  29
  30 // This type is a little tricky lifetime wise: Despite the fact that we're
  31 // talking about linked list of VaueWithSize, what is actually stored in the
  32 // list are dynamically allocated ValueWithSize*. As a result, these have to be
  33 // deleted. There are two ways this lifetime is managed:
  34 //
  35 // 1. In DequeueValue we pop the first element into a UniquePtr, so that it is
  36 //    correctly cleaned up at destruction time.
  37 // 2. We use an AutoCleanLinkedList which will delete elements when destroyed
  38 //    or `clear`ed.
  39 using QueueWithSizes = AutoCleanLinkedList<ValueWithSize>;
  40
  41 // https://streams.spec.whatwg.org/#is-non-negative-number
  42 inline bool IsNonNegativeNumber(double v) {
  43   // Step 1. Implicit.
  44   // Step 2.
  45   if (std::isnan(v)) {
  46     return false;
  47   }
  48
  49   // Step 3.
  50   return !(v < 0);
  51 }
  52
  53 // https://streams.spec.whatwg.org/#enqueue-value-with-size
  54 template <class QueueContainingClass>
  55 inline void EnqueueValueWithSize(QueueContainingClass aContainer,
  56                                  JS::Handle<JS::Value> aValue, double aSize,
  57                                  ErrorResult& aRv) {
  58   // Step 1. Assert: container has [[queue]] and [[queueTotalSize]] internal
  59   // slots. (Implicit by template instantiation.)
  60   // Step 2. If ! IsNonNegativeNumber(size) is false, throw a RangeError
  61   // exception.
  62   if (!IsNonNegativeNumber(aSize)) {
  63     aRv.ThrowRangeError("invalid size");
  64     return;
  65   }
  66
  67   // Step 3. If size is +∞, throw a RangeError exception.
  68   if (std::isinf(aSize)) {
  69     aRv.ThrowRangeError("Infinite queue size");
  70     return;
  71   }
  72
  73   // Step 4. Append a new value-with-size with value value and size size to
  74   // container.[[queue]].
  75   // (See the comment on QueueWithSizes for the lifetime reasoning around this
  76   // allocation.)
  77   ValueWithSize* valueWithSize = new ValueWithSize(aValue, aSize);
  78   aContainer->Queue().insertBack(valueWithSize);
  79   // Step 5. Set container.[[queueTotalSize]] to container.[[queueTotalSize]] +
  80   // size.
  81   aContainer->SetQueueTotalSize(aContainer->QueueTotalSize() + aSize);
  82 }
  83
  84 // https://streams.spec.whatwg.org/#dequeue-value
  85 template <class QueueContainingClass>
  86 inline void DequeueValue(QueueContainingClass aContainer,
  87                          JS::MutableHandle<JS::Value> aResultValue) {
  88   // Step 1. Implicit via template instantiation.
  89   // Step 2.
  90   MOZ_ASSERT(!aContainer->Queue().isEmpty());
  91
  92   // Step 3+4
  93   // UniquePtr to ensure memory is freed.
  94   UniquePtr<ValueWithSize> valueWithSize(aContainer->Queue().popFirst());
  95
  96   // Step 5.
  97   aContainer->SetQueueTotalSize(aContainer->QueueTotalSize() -
  98                                 valueWithSize->mSize);
  99
 100   // Step 6.
 101   if (aContainer->QueueTotalSize() < 0) {
 102     aContainer->SetQueueTotalSize(0);
 103   }
 104
 105   // Step 7.
 106   aResultValue.set(valueWithSize->mValue);
 107 }
 108
 109 // https://streams.spec.whatwg.org/#peek-queue-value
 110 template <class QueueContainingClass>
 111 inline void PeekQueueValue(QueueContainingClass aContainer,
 112                            JS::MutableHandle<JS::Value> aResultValue) {
 113   // Step 1. Assert: container has [[queue]] and [[queueTotalSize]] internal
 114   // slots.
 115   // Step 2. Assert: container.[[queue]] is not empty.
 116   MOZ_ASSERT(!aContainer->Queue().isEmpty());
 117
 118   // Step 3. Let valueWithSize be container.[[queue]][0].
 119   ValueWithSize* valueWithSize = aContainer->Queue().getFirst();
 120
 121   // Step 4. Return valueWithSize’s value.
 122   aResultValue.set(valueWithSize->mValue);
 123 }
 124
 125 // https://streams.spec.whatwg.org/#reset-queue
 126 template <class QueueContainingClass>
 127 inline void ResetQueue(QueueContainingClass aContainer) {
 128   // Step 1. Assert: container has [[queue]] and [[queueTotalSize]] internal
 129   // slots. (implicit)
 130
 131   // Step 2. Set container.[[queue]] to a new empty list.
 132   aContainer->Queue().clear();
 133
 134   // Step 3. Set container.[[queueTotalSize]] to 0.
 135   aContainer->SetQueueTotalSize(0.0);
 136 }
 137
 138 }  // namespace mozilla::dom
 139
 140 #endif