LibWeb: Support unique task sources

Some elements, like HTMLMediaElement, must have a unique task sources
for every instance of that element that is created. Support this with a
simple wrapper around IDAllocator.

2 files changed, 26 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/HTML/EventLoop/Task.cpp b/Userland/Libraries/LibWeb/HTML/EventLoop/Task.cpp
index 91f89765a4..60471f68d2 100644
--- a/Userland/Libraries/LibWeb/HTML/EventLoop/Task.cpp
+++ b/Userland/Libraries/LibWeb/HTML/EventLoop/Task.cpp
@@ -4,11 +4,14 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/IDAllocator.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/HTML/EventLoop/Task.h>
 
 namespace Web::HTML {
 
+static IDAllocator s_unique_task_source_allocator { static_cast<int>(Task::Source::UniqueTaskSourceStart) };
+
 Task::Task(Source source, DOM::Document const* document, JS::SafeFunction<void()> steps)
     : m_source(source)
     , m_steps(move(steps))
@@ -35,4 +38,14 @@ DOM::Document const* Task::document() const
     return m_document.ptr();
 }
 
+UniqueTaskSource::UniqueTaskSource()
+    : source(static_cast<Task::Source>(s_unique_task_source_allocator.allocate()))
+{
+}
+
+UniqueTaskSource::~UniqueTaskSource()
+{
+    s_unique_task_source_allocator.deallocate(static_cast<int>(source));
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/HTML/EventLoop/Task.h b/Userland/Libraries/LibWeb/HTML/EventLoop/Task.h
index a850df2152..98f8ca3b1e 100644
--- a/Userland/Libraries/LibWeb/HTML/EventLoop/Task.h
+++ b/Userland/Libraries/LibWeb/HTML/EventLoop/Task.h
@@ -15,6 +15,8 @@
 
 namespace Web::HTML {
 
+struct UniqueTaskSource;
+
 class Task {
 public:
     // https://html.spec.whatwg.org/multipage/webappapis.html#generic-task-sources
@@ -29,6 +31,10 @@ public:
         Microtask,
         TimerTask,
         JavaScriptEngine,
+
+        // Some elements, such as the HTMLMediaElement, must have a unique task source per instance.
+        // Keep this field last, to serve as the base value of all unique task sources.
+        UniqueTaskSourceStart,
     };
 
     static NonnullOwnPtr<Task> create(Source source, DOM::Document const* document, JS::SafeFunction<void()> steps)
@@ -52,4 +58,11 @@ private:
     JS::Handle<DOM::Document const> m_document;
 };
 
+struct UniqueTaskSource {
+    UniqueTaskSource();
+    ~UniqueTaskSource();
+
+    Task::Source const source;
+};
+
 }