Bug 1401827 - Baldr: make Fifo::pop infallible (r=lth)

MozReview-Commit-ID: Sc3Vuo97yZ

--HG--
extra : rebase_source : b32f9b2f148e0189026151d7355487f6adb9586e

js/src/ds/Fifo.h

@@ -46,19 +46,11 @@ class Fifo
 
   private:
     // Maintain invariants after adding or removing entries.
-    bool fixup() {
-        if (!front_.empty())
-            return true;
-
-        if (!front_.reserve(rear_.length()))
-            return false;
-
-        while (!rear_.empty()) {
-            front_.infallibleAppend(mozilla::Move(rear_.back()));
-            rear_.popBack();
+    void fixup() {
+        if (front_.empty() && !rear_.empty()) {
+            front_.swap(rear_);
+            Reverse(front_.begin(), front_.end());
         }
-
-        return true;
     }
 
   public:
@@ -98,10 +90,7 @@ class Fifo
     MOZ_MUST_USE bool pushBack(U&& u) {
         if (!rear_.append(mozilla::Forward<U>(u)))
             return false;
-        if (!fixup()) {
-            rear_.popBack();
-            return false;
-        }
+        fixup();
         return true;
     }
 
@@ -110,10 +99,7 @@ class Fifo
     MOZ_MUST_USE bool emplaceBack(Args&&... args) {
         if (!rear_.emplaceBack(mozilla::Forward<Args>(args)...))
             return false;
-        if (!fixup()) {
-            rear_.popBack();
-            return false;
-        }
+        fixup();
         return true;
     }
 
@@ -128,20 +114,10 @@ class Fifo
     }
 
     // Remove the front element from the queue.
-    MOZ_MUST_USE bool popFront() {
+    void popFront() {
         MOZ_ASSERT(!empty());
-        T t(mozilla::Move(front()));
         front_.popBack();
-        if (!fixup()) {
-            // Attempt to remain in a valid state by reinserting the element
-            // back at the front. If we can't remain in a valid state in the
-            // face of OOMs, crash.
-            AutoEnterOOMUnsafeRegion oomUnsafe;
-            if (!front_.append(mozilla::Move(t)))
-                oomUnsafe.crash("js::Fifo::popFront");
-            return false;
-        }
-        return true;
+        fixup();
     }
 
     // Clear all elements from the queue.

js/src/ds/TraceableFifo.h

@@ -79,7 +79,7 @@ class MutableWrappedPtrOperations<TraceableFifo<T, Capacity, AllocPolicy>, Wrapp
         return fifo().emplaceBack(mozilla::Forward<Args...>(args...));
     }
 
-    bool popFront() { return fifo().popFront(); }
+    void popFront() { fifo().popFront(); }
     void clear() { fifo().clear(); }
 };
 

js/src/jsapi-tests/testGCExactRooting.cpp

@@ -323,7 +323,7 @@ BEGIN_TEST(testTraceableFifo)
         bool match;
         CHECK(JS_StringEqualsAscii(cx, JSID_TO_STRING(shapes.front()->propid()), buffer, &match));
         CHECK(match);
-        CHECK(shapes.popFront());
+        shapes.popFront();
     }
 
     CHECK(shapes.empty());

js/src/vm/Debugger.cpp

@@ -2298,10 +2298,7 @@ Debugger::appendAllocationSite(JSContext* cx, HandleObject obj, HandleSavedFrame
     }
 
     if (allocationsLog.length() > maxAllocationsLogLength) {
-        if (!allocationsLog.popFront()) {
-            ReportOutOfMemory(cx);
-            return false;
-        }
+        allocationsLog.popFront();
         MOZ_ASSERT(allocationsLog.length() == maxAllocationsLogLength);
         allocationsLogOverflowed = true;
     }

js/src/vm/DebuggerMemory.cpp

@@ -238,10 +238,7 @@ DebuggerMemory::drainAllocationsLog(JSContext* cx, unsigned argc, Value* vp)
         // Pop the front queue entry, and delete it immediately, so that the GC
         // sees the AllocationsLogEntry's HeapPtr barriers run atomically with
         // the change to the graph (the queue link).
-        if (!dbg->allocationsLog.popFront()) {
-            ReportOutOfMemory(cx);
-            return false;
-        }
+        dbg->allocationsLog.popFront();
     }
 
     dbg->allocationsLogOverflowed = false;
@@ -278,12 +275,8 @@ DebuggerMemory::setMaxAllocationsLogLength(JSContext* cx, unsigned argc, Value*
     Debugger* dbg = memory->getDebugger();
     dbg->maxAllocationsLogLength = max;
 
-    while (dbg->allocationsLog.length() > dbg->maxAllocationsLogLength) {
-        if (!dbg->allocationsLog.popFront()) {
-            ReportOutOfMemory(cx);
-            return false;
-        }
-    }
+    while (dbg->allocationsLog.length() > dbg->maxAllocationsLogLength)
+        dbg->allocationsLog.popFront();
 
     args.rval().setUndefined();
     return true;