Use std::atomic in Cancelable

Avoid deprecated base::AtomicValue, use std::atomic instead.
Plus minor drive-by cleanups.

R=mstarzinger@chromium.org

Bug: v8:8238
Change-Id: I47a1f00e26a843b60380c50399eedc49d859830a
Reviewed-on: https://chromium-review.googlesource.com/c/1326463
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57386}

src/cancelable-task.cc

@@ -10,18 +10,12 @@
 namespace v8 {
 namespace internal {
 
-
-Cancelable::Cancelable(CancelableTaskManager* parent)
-    : parent_(parent), status_(kWaiting), id_(0), cancel_counter_(0) {
-  id_ = parent->Register(this);
-}
-
-
 Cancelable::~Cancelable() {
   // The following check is needed to avoid calling an already terminated
   // manager object. This happens when the manager cancels all pending tasks
   // in {CancelAndWait} only before destroying the manager object.
-  if (TryRun() || IsRunning()) {
+  Status previous;
+  if (TryRun(&previous) || previous == kRunning) {
     parent_->RemoveFinishedTask(id_);
   }
 }

src/cancelable-task.h

@@ -5,10 +5,10 @@
 #ifndef V8_CANCELABLE_TASK_H_
 #define V8_CANCELABLE_TASK_H_
 
+#include <atomic>
 #include <unordered_map>
 
 #include "include/v8-platform.h"
-#include "src/base/atomic-utils.h"
 #include "src/base/macros.h"
 #include "src/base/platform/condition-variable.h"
 #include "src/globals.h"
@@ -86,7 +86,9 @@ class V8_EXPORT_PRIVATE CancelableTaskManager {
 
 class V8_EXPORT_PRIVATE Cancelable {
  public:
-  explicit Cancelable(CancelableTaskManager* parent);
+  explicit Cancelable(CancelableTaskManager* parent)
+      : parent_(parent), id_(parent->Register(this)) {}
+
   virtual ~Cancelable();
 
   // Never invoke after handing over the task to the platform! The reason is
@@ -97,42 +99,48 @@ class V8_EXPORT_PRIVATE Cancelable {
   CancelableTaskManager::Id id() { return id_; }
 
  protected:
-  bool TryRun() { return status_.TrySetValue(kWaiting, kRunning); }
-  bool IsRunning() { return status_.Value() == kRunning; }
-  intptr_t CancelAttempts() { return cancel_counter_; }
-
- private:
   // Identifies the state a cancelable task is in:
   // |kWaiting|: The task is scheduled and waiting to be executed. {TryRun} will
   //   succeed.
   // |kCanceled|: The task has been canceled. {TryRun} will fail.
   // |kRunning|: The task is currently running and cannot be canceled anymore.
-  enum Status {
-    kWaiting,
-    kCanceled,
-    kRunning,
-  };
+  enum Status { kWaiting, kCanceled, kRunning };
+
+  bool TryRun(Status* previous = nullptr) {
+    return CompareExchangeStatus(kWaiting, kRunning, previous);
+  }
+  intptr_t CancelAttempts() { return cancel_counter_; }
+
+ private:
+  friend class CancelableTaskManager;
 
   // Use {CancelableTaskManager} to abort a task that has not yet been
   // executed.
   bool Cancel() {
-    if (status_.TrySetValue(kWaiting, kCanceled)) {
+    if (CompareExchangeStatus(kWaiting, kCanceled)) {
       return true;
     }
     cancel_counter_++;
     return false;
   }
 
-  CancelableTaskManager* parent_;
-  base::AtomicValue<Status> status_;
-  CancelableTaskManager::Id id_;
+  bool CompareExchangeStatus(Status expected, Status desired,
+                             Status* previous = nullptr) {
+    // {compare_exchange_strong} updates {expected}.
+    bool success = status_.compare_exchange_strong(expected, desired,
+                                                   std::memory_order_relaxed);
+    if (previous) *previous = expected;
+    return success;
+  }
+
+  CancelableTaskManager* const parent_;
+  std::atomic<Status> status_{kWaiting};
+  const CancelableTaskManager::Id id_;
 
   // The counter is incremented for failing tries to cancel a task. This can be
   // used by the task itself as an indication how often external entities tried
   // to abort it.
-  std::atomic<intptr_t> cancel_counter_;
-
-  friend class CancelableTaskManager;
+  std::atomic<intptr_t> cancel_counter_{0};
 
   DISALLOW_COPY_AND_ASSIGN(Cancelable);
 };