1 files changed, 41 insertions, 0 deletions
diff --git a/xpcom/threads/nsIDiscardableRunnable.h b/xpcom/threads/nsIDiscardableRunnable.h
new file mode 100644
index 0000000000..873b1f5d93
--- /dev/null
+++ b/xpcom/threads/nsIDiscardableRunnable.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef XPCOM_THREADS_NSIDISCARDABLERUNNABLE_H_
+#define XPCOM_THREADS_NSIDISCARDABLERUNNABLE_H_
+
+#include "nsISupports.h"
+
+/**
+ * An interface implemented by nsIRunnable tasks for which nsIRunnable::Run()
+ * might not be called.
+ */
+#define NS_IDISCARDABLERUNNABLE_IID                  \
+  {                                                  \
+    0xde93dc4c, 0x755c, 0x4cdc, {                    \
+      0x96, 0x76, 0x35, 0xc6, 0x48, 0x81, 0x59, 0x78 \
+    }                                                \
+  }
+
+class NS_NO_VTABLE nsIDiscardableRunnable : public nsISupports {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_IDISCARDABLERUNNABLE_IID)
+
+  /**
+   * Called exactly once on a queued task only if nsIRunnable::Run() is not
+   * called.
+   */
+  virtual void OnDiscard() = 0;
+
+ protected:
+  nsIDiscardableRunnable() = default;
+  virtual ~nsIDiscardableRunnable() = default;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsIDiscardableRunnable,
+                              NS_IDISCARDABLERUNNABLE_IID)
+
+#endif  // XPCOM_THREADS_NSIDISCARDABLERUNNABLE_H_