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src/base/task_runner.cc

@@ -20,6 +20,10 @@ void PostTaskAndReplyRelay(base::Location from,
 
 namespace base {
 
+// The task runner that belongs to the thread it's created in. Tasks to be run
+// on a specific thread can be posted to this task runner.
+// TaskRunner::GetThreadLocalTaskRunner()->SingleConsumerRun() is expected to be
+// periodically called.
 thread_local std::unique_ptr<TaskRunner> TaskRunner::thread_local_task_runner;
 
 void TaskRunner::CreateThreadLocalTaskRunner() {

src/base/task_runner.h

@@ -34,9 +34,9 @@ void ReplyAdapter(std::function<void(ReturnType)> callback,
 
 // Runs queued tasks (in the form of Closure objects). All methods are
 // thread-safe and can be called on any thread.
-// Tasks run in FIFO order. When consumed concurrently by multiple threads, it
-// doesn't guarantee whether tasks overlap, or whether they run on a particular
-// thread.
+// Tasks run in FIFO order when consumed by a single thread. When consumed
+// concurrently by multiple threads, it doesn't guarantee whether tasks overlap,
+// or whether they run on a particular thread.
 class TaskRunner {
  public:
   TaskRunner() = default;