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 "js/TypeDecls.h"
  11 #include "js/Value.h"
  12 #include "mozilla/ErrorResult.h"
  13 #include "mozilla/FloatingPoint.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 (mozilla::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. Implicit by template instantiation.
  59   // Step 2.
  60   if (!IsNonNegativeNumber(aSize)) {
  61     aRv.ThrowRangeError("invalid size");
  62     return;
  63   }
  64
  65   // Step 3.
  66   if (mozilla::IsInfinite(aSize)) {
  67     aRv.ThrowRangeError("Infinite queue size");
  68     return;
  69   }
  70
  71   // Step 4. See the comment on QueueWithSizes for the lifetime reasoning
  72   //         around this allocation.
  73   ValueWithSize* valueWithSize = new ValueWithSize(aValue, aSize);
  74   aContainer->Queue().insertBack(valueWithSize);
  75   // Step 5.
  76   aContainer->SetQueueTotalSize(aContainer->QueueTotalSize() + aSize);
  77 }
  78
  79 // https://streams.spec.whatwg.org/#dequeue-value
  80 template <class QueueContainingClass>
  81 inline void DequeueValue(QueueContainingClass aContainer,
  82                          JS::MutableHandle<JS::Value> aResultValue) {
  83   // Step 1. Implicit via template instantiation.
  84   // Step 2.
  85   MOZ_ASSERT(!aContainer->Queue().isEmpty());
  86
  87   // Step 3+4
  88   // UniquePtr to ensure memory is freed.
  89   UniquePtr<ValueWithSize> valueWithSize(aContainer->Queue().popFirst());
  90
  91   // Step 5.
  92   aContainer->SetQueueTotalSize(aContainer->QueueTotalSize() -
  93                                 valueWithSize->mSize);
  94
  95   // Step 6.
  96   if (aContainer->QueueTotalSize() < 0) {
  97     aContainer->SetQueueTotalSize(0);
  98   }
  99
 100   // Step 7.
 101   aResultValue.set(valueWithSize->mValue);
 102 }
 103
 104 // https://streams.spec.whatwg.org/#peek-queue-value
 105 template <class QueueContainingClass>
 106 inline void PeekQueueValue(QueueContainingClass aContainer,
 107                            JS::MutableHandle<JS::Value> aResultValue) {
 108   // Step 1. Assert: container has [[queue]] and [[queueTotalSize]] internal
 109   // slots.
 110   // Step 2. Assert: container.[[queue]] is not empty.
 111   MOZ_ASSERT(!aContainer->Queue().isEmpty());
 112
 113   // Step 3. Let valueWithSize be container.[[queue]][0].
 114   ValueWithSize* valueWithSize = aContainer->Queue().getFirst();
 115
 116   // Step 4. Return valueWithSize’s value.
 117   aResultValue.set(valueWithSize->mValue);
 118 }
 119
 120 // https://streams.spec.whatwg.org/#reset-queue
 121 template <class QueueContainingClass>
 122 inline void ResetQueue(QueueContainingClass aContainer) {
 123   // Step 1. Assert: container has [[queue]] and [[queueTotalSize]] internal
 124   // slots. (implicit)
 125
 126   // Step 2. Set container.[[queue]] to a new empty list.
 127   aContainer->Queue().clear();
 128
 129   // Step 3. Set container.[[queueTotalSize]] to 0.
 130   aContainer->SetQueueTotalSize(0.0);
 131 }
 132
 133 }  // namespace mozilla::dom
 134
 135 #endif