diff -r 000000000000 -r 6474c204b198 js/public/SliceBudget.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/public/SliceBudget.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,57 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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 js_SliceBudget_h
+#define js_SliceBudget_h
+
+#include <stdint.h>
+
+namespace js {
+
+/*
+ * This class records how much work has been done in a given collection slice, so that
+ * we can return before pausing for too long. Some slices are allowed to run for
+ * unlimited time, and others are bounded. To reduce the number of gettimeofday
+ * calls, we only check the time every 1000 operations.
+ */
+struct JS_PUBLIC_API(SliceBudget)
+{
+    int64_t deadline; /* in microseconds */
+    intptr_t counter;
+
+    static const intptr_t CounterReset = 1000;
+
+    static const int64_t Unlimited = 0;
+    static int64_t TimeBudget(int64_t millis);
+    static int64_t WorkBudget(int64_t work);
+
+    /* Equivalent to SliceBudget(UnlimitedBudget). */
+    SliceBudget();
+
+    /* Instantiate as SliceBudget(Time/WorkBudget(n)). */
+    SliceBudget(int64_t budget);
+
+    void reset() {
+        deadline = INT64_MAX;
+        counter = INTPTR_MAX;
+    }
+
+    void step(intptr_t amt = 1) {
+        counter -= amt;
+    }
+
+    bool checkOverBudget();
+
+    bool isOverBudget() {
+        if (counter >= 0)
+            return false;
+        return checkOverBudget();
+    }
+};
+
+} // namespace js
+
+#endif /* js_SliceBudget_h */