Bug 1438121: Final Part 1: Change JS::CopyAsyncStack's maxFrameCount to be a Maybe, and use that type throughout. r=tromey
authorJim Blandy <jimb@mozilla.com>
Tue, 06 Mar 2018 21:52:31 -0800
changeset 407432 b621eecdca37582f8bc6872e7ed096be85203334
parent 407431 1976ff94b12a14e32cac357c1ef2cf7caca8ff7e
child 407433 f54675bcf897379cd4f81cad3b80f812b9f2a903
push id100691
push userjblandy@mozilla.com
push dateSat, 10 Mar 2018 02:26:54 +0000
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Bug 1438121: Final Part 1: Change JS::CopyAsyncStack's maxFrameCount to be a Maybe, and use that type throughout. r=tromey I botched another patch in this series because I was confused about when zero meant "no limit" and when it actually just meant zero, so I figured I'd fix this. MozReview-Commit-ID: 5vgzKGSKL8F
--- a/docshell/base/timeline/JavascriptTimelineMarker.h
+++ b/docshell/base/timeline/JavascriptTimelineMarker.h
@@ -3,16 +3,19 @@
 /* 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 mozilla_JavascriptTimelineMarker_h_
 #define mozilla_JavascriptTimelineMarker_h_
 #include "TimelineMarker.h"
+#include "mozilla/Maybe.h"
 #include "mozilla/dom/ProfileTimelineMarkerBinding.h"
 #include "mozilla/dom/RootedDictionary.h"
 #include "mozilla/dom/ToJSValue.h"
 namespace mozilla {
 class JavascriptTimelineMarker : public TimelineMarker
@@ -58,17 +61,17 @@ public:
         JS::Rooted<JSString*> asyncCause(aCx, JS_NewUCStringCopyN(aCx, mAsyncCause.BeginReading(),
         if (!asyncCause) {
         if (JS::IsSavedFrame(asyncStack) &&
-            !JS::CopyAsyncStack(aCx, asyncStack, asyncCause, &parentFrame, 0)) {
+            !JS::CopyAsyncStack(aCx, asyncStack, asyncCause, &parentFrame, mozilla::Nothing())) {
         } else {
           stackFrame.mAsyncParent = parentFrame;
       JS::Rooted<JS::Value> newStack(aCx);
       if (ToJSValue(aCx, stackFrame, &newStack)) {
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -7756,17 +7756,17 @@ JS::CaptureCurrentStack(JSContext* cx, J
         return false;
     return true;
 JS::CopyAsyncStack(JSContext* cx, JS::HandleObject asyncStack,
                    JS::HandleString asyncCause, JS::MutableHandleObject stackp,
-                   unsigned maxFrameCount)
+                   const Maybe<size_t>& maxFrameCount)
     js::AssertObjectIsSavedFrameOrWrapper(cx, asyncStack);
     JSCompartment* compartment = cx->compartment();
     Rooted<SavedFrame*> frame(cx);
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -6502,24 +6502,24 @@ CaptureCurrentStack(JSContext* cx, Mutab
  * by some other object.  This may be used when you need to treat a
  * given stack trace as an async parent.  If you just need to capture
  * the current stack, async parents and all, use CaptureCurrentStack
  * instead.
  * Here |asyncStack| is the async stack to prepare.  It is copied into
  * |cx|'s current compartment, and the newest frame is given
  * |asyncCause| as its asynchronous cause.  If |maxFrameCount| is
- * non-zero, capture at most the youngest |maxFrameCount| frames.  The
+ * |Some(n)|, capture at most the youngest |n| frames.  The
  * new stack object is written to |stackp|.  Returns true on success,
  * or sets an exception and returns |false| on error.
 extern JS_PUBLIC_API(bool)
 CopyAsyncStack(JSContext* cx, HandleObject asyncStack,
                HandleString asyncCause, MutableHandleObject stackp,
-               unsigned maxFrameCount);
+               const mozilla::Maybe<size_t>& maxFrameCount);
  * Accessors for working with SavedFrame JSObjects
  * Each of these functions assert that if their `HandleObject savedFrame`
  * argument is non-null, its JSClass is the SavedFrame class (or it is a
  * cross-compartment or Xray wrapper around an object with the SavedFrame class)
  * and the object is not the SavedFrame.prototype object.
--- a/js/src/vm/SavedStacks.cpp
+++ b/js/src/vm/SavedStacks.cpp
@@ -1185,17 +1185,18 @@ SavedStacks::saveCurrentStack(JSContext*
     AutoGeckoProfilerEntry pseudoFrame(cx, "js::SavedStacks::saveCurrentStack");
     FrameIter iter(cx);
     return insertFrames(cx, iter, frame, mozilla::Move(capture));
 SavedStacks::copyAsyncStack(JSContext* cx, HandleObject asyncStack, HandleString asyncCause,
-                            MutableHandleSavedFrame adoptedStack, uint32_t maxFrameCount)
+                            MutableHandleSavedFrame adoptedStack,
+                            const Maybe<size_t>& maxFrameCount)
     assertSameCompartment(cx, this);
     RootedObject asyncStackObj(cx, CheckedUnwrap(asyncStack));
@@ -1406,20 +1407,20 @@ SavedStacks::insertFrames(JSContext* cx,
     // Limit the depth of the async stack, if any, and ensure that the
     // SavedFrame instances we use are stored in the same compartment as the
     // rest of the synchronous stack chain.
     RootedSavedFrame parentFrame(cx, cachedFrame);
     if (asyncStack && !capture.is<JS::FirstSubsumedFrame>()) {
-        uint32_t maxAsyncFrames = capture.is<JS::MaxFrames>()
+        size_t maxAsyncFrames = capture.is<JS::MaxFrames>()
             ? capture.as<JS::MaxFrames>().maxFrames
-        if (!adoptAsyncStack(cx, asyncStack, asyncCause, &parentFrame, maxAsyncFrames))
+        if (!adoptAsyncStack(cx, asyncStack, asyncCause, &parentFrame, Some(maxAsyncFrames)))
             return false;
     // Iterate through |stackChain| in reverse order and get or create the
     // actual SavedFrame instances.
     for (size_t i = stackChain->length(); i != 0; i--) {
         SavedFrame::HandleLookup lookup = stackChain[i-1];
         lookup->parent = parentFrame;
@@ -1437,27 +1438,27 @@ SavedStacks::insertFrames(JSContext* cx,
     return true;
 SavedStacks::adoptAsyncStack(JSContext* cx, HandleSavedFrame asyncStack,
                              HandleString asyncCause,
                              MutableHandleSavedFrame adoptedStack,
-                             uint32_t maxFrameCount)
+                             const Maybe<size_t>& maxFrameCount)
     RootedAtom asyncCauseAtom(cx, AtomizeString(cx, asyncCause));
     if (!asyncCauseAtom)
         return false;
-    // If maxFrameCount is zero, the caller asked for an unlimited number of
+    // If maxFrameCount is Nothing, the caller asked for an unlimited number of
     // stack frames, but async stacks are not limited by the available stack
     // memory, so we need to set an arbitrary limit when collecting them. We
     // still don't enforce an upper limit if the caller requested more frames.
-    uint32_t maxFrames = maxFrameCount > 0 ? maxFrameCount : ASYNC_STACK_MAX_FRAME_COUNT;
+    size_t maxFrames = maxFrameCount.valueOr(ASYNC_STACK_MAX_FRAME_COUNT);
     // Accumulate the vector of Lookup objects in |stackChain|.
     SavedFrame::AutoLookupVector stackChain(cx);
     SavedFrame* currentSavedFrame = asyncStack;
     SavedFrame* firstSavedFrameParent = nullptr;
     for (uint32_t i = 0; i < maxFrames && currentSavedFrame; i++) {
         if (!stackChain->emplaceBack(*currentSavedFrame)) {
@@ -1480,17 +1481,17 @@ SavedStacks::adoptAsyncStack(JSContext* 
     if (currentSavedFrame == nullptr &&
         asyncStack->compartment() == cx->compartment()) {
         // If we consumed the full async stack, and the stack is in the same
         // compartment as the one requested, we don't need to rebuild the full
         // chain again using the lookup objects, we can just reference the
         // existing chain and change the asyncCause on the younger frame.
         oldestFramePosition = 1;
         parentFrame = firstSavedFrameParent;
-    } else if (maxFrameCount == 0 &&
+    } else if (maxFrameCount.isNothing() &&
                oldestFramePosition == ASYNC_STACK_MAX_FRAME_COUNT) {
         // If we captured the maximum number of frames and the caller requested
         // no specific limit, we only return half of them. This means that for
         // the next iterations, it's likely we can use the optimization above.
         oldestFramePosition = ASYNC_STACK_MAX_FRAME_COUNT / 2;
     // Iterate through |stackChain| in reverse order and get or create the
--- a/js/src/vm/SavedStacks.h
+++ b/js/src/vm/SavedStacks.h
@@ -165,17 +165,17 @@ class SavedStacks {
     MOZ_MUST_USE bool init();
     bool initialized() const { return frames.initialized(); }
     MOZ_MUST_USE bool saveCurrentStack(JSContext* cx, MutableHandleSavedFrame frame,
                                        JS::StackCapture&& capture = JS::StackCapture(JS::AllFrames()));
     MOZ_MUST_USE bool copyAsyncStack(JSContext* cx, HandleObject asyncStack,
                                      HandleString asyncCause,
                                      MutableHandleSavedFrame adoptedStack,
-                                     uint32_t maxFrameCount = 0);
+                                     const Maybe<size_t>& maxFrameCount);
     void sweep();
     void trace(JSTracer* trc);
     uint32_t count();
     void clear();
     void chooseSamplingProbability(JSCompartment*);
     // Set the sampling random number generator's state to |state0| and
     // |state1|. One or the other must be non-zero. See the comments for
@@ -221,17 +221,17 @@ class SavedStacks {
     MOZ_MUST_USE bool insertFrames(JSContext* cx, FrameIter& iter,
                                    MutableHandleSavedFrame frame,
                                    JS::StackCapture&& capture);
     MOZ_MUST_USE bool adoptAsyncStack(JSContext* cx, HandleSavedFrame asyncStack,
                                       HandleString asyncCause,
                                       MutableHandleSavedFrame adoptedStack,
-                                      uint32_t maxFrameCount);
+                                      const Maybe<size_t>& maxFrameCount);
     SavedFrame* getOrCreateSavedFrame(JSContext* cx, SavedFrame::HandleLookup lookup);
     SavedFrame* createFrameFromLookup(JSContext* cx, SavedFrame::HandleLookup lookup);
     // Cache for memoizing PCToLineNumber lookups.
     struct PCKey {
         PCKey(JSScript* script, jsbytecode* pc) : script(script), pc(pc) { }