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Document DeferredHandleScope

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R=jochen@chromium.org

Change-Id: I34bc156c3c4911ba8511ba9720fb6cc2e3880d7e
Reviewed-on: https://chromium-review.googlesource.com/468888
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44407}
This commit is contained in:
Andreas Haas 2017-04-05 13:00:56 +02:00 committed by Commit Bot
parent eeaceccbc6
commit ab56c22339
2 changed files with 24 additions and 1 deletions
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3
src/handles.cc
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@ -167,6 +167,9 @@ DeferredHandleScope::DeferredHandleScope(Isolate* isolate)
HandleScopeData* data = impl_->isolate()->handle_scope_data();
Object** new_next = impl_->GetSpareOrNewBlock();
Object** new_limit = &new_next[kHandleBlockSize];
// Check that at least one HandleScope exists, see the class description.
DCHECK(!impl_->blocks()->is_empty());
// Check that we are not in a SealedHandleScope.
DCHECK(data->limit == &impl_->blocks()->last()[kHandleBlockSize]);
impl_->blocks()->Add(new_next);

22
src/handles.h
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@ -354,6 +354,26 @@ class V8_EXPORT_PRIVATE CanonicalHandleScope final {
friend class HandleScope;
};
// A DeferredHandleScope is a HandleScope in which handles are not destroyed
// when the DeferredHandleScope is left. Instead the DeferredHandleScope has to
// be detached with {Detach}, and the result of {Detach} has to be destroyed
// explicitly. A DeferredHandleScope should only be used with the following
// design pattern:
// 1) Open a HandleScope (not a DeferredHandleScope).
// HandleScope scope(isolate_);
// 2) Create handles.
// Handle<Object> h1 = handle(object1, isolate);
// Handle<Object> h2 = handle(object2, isolate);
// 3) Open a DeferredHandleScope.
// DeferredHandleScope deferred_scope(isolate);
// 4) Reopen handles which should be in the DeferredHandleScope, e.g only h1.
// h1 = handle(*h1, isolate);
// 5) Detach the DeferredHandleScope.
// DeferredHandles* deferred_handles = deferred_scope.Detach();
// 6) Destroy the deferred handles.
// delete deferred_handles;
//
// Note: A DeferredHandleScope must not be opened within a DeferredHandleScope.
class V8_EXPORT_PRIVATE DeferredHandleScope final {
public:
explicit DeferredHandleScope(Isolate* isolate);
@ -369,7 +389,7 @@ class V8_EXPORT_PRIVATE DeferredHandleScope final {
HandleScopeImplementer* impl_;
#ifdef DEBUG
bool handles_detached_;
bool handles_detached_ = false;
int prev_level_;
#endif