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Bug 1209704 - Part 4: Add a post-barrier to ReadBarriered; r=jonco

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This commit is contained in:
Terrence Cole 2015-09-29 13:03:52 -07:00
parent b537ca8112
commit 2b432e9326
1 changed files with 20 additions and 5 deletions
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25
js/src/gc/Barrier.h
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@ -528,7 +528,7 @@ class RelocatablePtr : public WriteBarrieredBase<T>
}
};
// Base class for barriered pointer types that intercept only reads.
// Base class for barriered pointer types that intercept reads and writes.
template <typename T>
class ReadBarrieredBase : public BarrieredBase<T>
{
@ -538,6 +538,7 @@ class ReadBarrieredBase : public BarrieredBase<T>
protected:
void read() const { InternalGCMethods<T>::readBarrier(this->value); }
void post(T prev, T next) { InternalGCMethods<T>::postBarrier(&this->value, prev, next); }
};
// Incremental GC requires that weak pointers have read barriers. This is mostly
@ -548,12 +549,22 @@ class ReadBarrieredBase : public BarrieredBase<T>
// when the GC started. However, since this is a weak pointer, it isn't. So we
// may collect the empty shape even though a live object points to it. To fix
// this, we mark these empty shapes black whenever they get read out.
template <class T>
//
// Note that this class also has post-barriers, so is safe to use with nursery
// pointers. However, when used as a hashtable key, care must still be taken to
// insert manual post-barriers on the table for rekeying if the key is based in
// any way on the address of the object.
template <typename T>
class ReadBarriered : public ReadBarrieredBase<T>
{
public:
ReadBarriered() : ReadBarrieredBase<T>(GCMethods<T>::initial()) {}
explicit ReadBarriered(const T& v) : ReadBarrieredBase<T>(v) {}
explicit ReadBarriered(const T& v) : ReadBarrieredBase<T>(v) {
this->post(GCMethods<T>::initial(), v);
}
~ReadBarriered() {
this->post(this->value, GCMethods<T>::initial());
}
const T get() const {
if (!InternalGCMethods<T>::isMarkable(this->value))
@ -568,12 +579,16 @@ class ReadBarriered : public ReadBarrieredBase<T>
operator const T() const { return get(); }
const T& operator*() const { return *get(); }
const T operator->() const { return get(); }
T const* unsafeGet() const { return &this->value; }
void set(const T& v) { this->value = v; }
void set(const T& v)
{
T tmp = this->value;
this->value = v;
this->post(tmp, v);
}
};
// Add Value operations to all Barrier types. Note, this must be defined before