[API] Enforce that ShouldYield == true is respected

There is a DCHECK in the gin platform that {ShouldYield} is not called
again after it already returned {true}.
This CL adds a similar DCHECK to the default platform to catch bugs
earlier (in d8).

R=ahaas@chromium.org, mlippautz@chromium.org

Bug: chromium:1277962
Change-Id: I4dc9d880cf6d36e3e497c5324aaf44889fe7fcee
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3644801Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80611}

include/v8-platform.h

@@ -158,9 +158,10 @@ class TaskRunner {
 class JobDelegate {
  public:
   /**
-   * Returns true if this thread should return from the worker task on the
+   * Returns true if this thread *must* return from the worker task on the
    * current thread ASAP. Workers should periodically invoke ShouldYield (or
    * YieldIfNeeded()) as often as is reasonable.
+   * After this method returned true, ShouldYield must not be called again.
    */
   virtual bool ShouldYield() = 0;
 

src/libplatform/default-job.h

@@ -29,8 +29,14 @@ class V8_PLATFORM_EXPORT DefaultJobState
       outer_->NotifyConcurrencyIncrease();
     }
     bool ShouldYield() override {
+      // After {ShouldYield} returned true, the job is expected to return and
+      // not call {ShouldYield} again. This resembles a similar DCHECK in the
+      // gin platform.
+      DCHECK(!was_told_to_yield_);
       // Thread-safe but may return an outdated result.
-      return outer_->is_canceled_.load(std::memory_order_relaxed);
+      was_told_to_yield_ |=
+          outer_->is_canceled_.load(std::memory_order_relaxed);
+      return was_told_to_yield_;
     }
     uint8_t GetTaskId() override;
     bool IsJoiningThread() const override { return is_joining_thread_; }
@@ -42,6 +48,7 @@ class V8_PLATFORM_EXPORT DefaultJobState
     DefaultJobState* outer_;
     uint8_t task_id_ = kInvalidTaskId;
     bool is_joining_thread_;
+    bool was_told_to_yield_ = false;
   };
 
   DefaultJobState(Platform* platform, std::unique_ptr<JobTask> job_task,