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Bug 754146: Root *all* the objects we encounter while reversing the heap. r=billm

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This commit is contained in:
Jim Blandy 2012-05-22 12:16:17 -07:00
parent a4f74fd15b
commit 5257898053
1 changed files with 21 additions and 10 deletions
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31
js/src/shell/jsheaptools.cpp
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@ -148,10 +148,16 @@ class HeapReverser : public JSTracer {
private:
/*
* Conservative scanning can, on a whim, decide that a root is no longer a
* root, and cause bits of our graph to disappear. The 'roots' vector holds
* all the roots we find alive, and 'rooter' keeps them alive until we're
* destroyed.
* Once we've produced a reversed map of the heap, we need to keep the
* engine from freeing the objects we've found in it, until we're done using
* the map. Even if we're only using the map to construct a result object,
* and not rearranging the heap ourselves, any allocation could cause a
* garbage collection, which could free objects held internally by the
* engine (for example, JaegerMonkey object templates, used by jit scripts).
*
* So, each time reverseHeap reaches any object, we add it to 'roots', which
* is cited by 'rooter', so the object will stay alive long enough for us to
* include it in the results, if needed.
*
* Note that AutoArrayRooters must be constructed and destroyed in a
* stack-like order, so the same rule applies to this HeapReverser. The
@ -218,7 +224,8 @@ class HeapReverser : public JSTracer {
/* Static member function wrapping 'traverseEdge'. */
static void traverseEdgeWithThis(JSTracer *tracer, void **thingp, JSGCTraceKind kind) {
HeapReverser *reverser = static_cast<HeapReverser *>(tracer);
reverser->traversalStatus = reverser->traverseEdge(*thingp, kind);
if (!reverser->traverseEdge(*thingp, kind))
reverser->traversalStatus = false;
}
/* Return a jsval representing a node, if possible; otherwise, return JSVAL_VOID. */
@ -231,10 +238,11 @@ class HeapReverser : public JSTracer {
};
bool
HeapReverser::traverseEdge(void *cell, JSGCTraceKind kind) {
/* If this is a root, make our own root for it as well. */
if (!parent) {
if (!roots.append(nodeToValue(cell, kind)))
HeapReverser::traverseEdge(void *cell, JSGCTraceKind kind)
{
jsval v = nodeToValue(cell, kind);
if (v.isObject()) {
if (!roots.append(v))
return false;
rooter.changeArray(roots.begin(), roots.length());
}
@ -267,7 +275,10 @@ HeapReverser::traverseEdge(void *cell, JSGCTraceKind kind) {
}
bool
HeapReverser::reverseHeap() {
HeapReverser::reverseHeap()
{
traversalStatus = true;
/* Prime the work stack with the roots of collection. */
JS_TraceRuntime(this);
if (!traversalStatus)