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[top-level-await] Implement the new post-order requirement for async subgraphs
This CL implements tc39/proposal-top-level-await#159, which reached consensus at the March 2021 TC39. The high-level intent is for parent modules that depend on async modules to remember the DFS post-order such that when their async dependency finishes, they execute in that original post-order. This aligns the ordering between completely sync module graphs and async module graphs. Bug: v8:11557 Change-Id: I5bd8f38f040115c255ca1ce8253b9686fdb4af03 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2757901 Commit-Queue: Shu-yu Guo <syg@chromium.org> Reviewed-by: Camillo Bruni <cbruni@chromium.org> Reviewed-by: Adam Klein <adamk@chromium.org> Cr-Commit-Position: refs/heads/master@{#73551}
1 parent 341ab4d commit f19142e

17 files changed

Lines changed: 335 additions & 87 deletions

‎src/common/globals.h‎

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@@ -365,6 +365,9 @@ constexpr int kUC16Size = sizeof(uc16); // NOLINT
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// 128 bit SIMD value size.
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constexpr int kSimd128Size = 16;
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// Maximum ordinal used for tracking asynchronous module evaluation order.
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constexpr unsigned kMaxModuleAsyncEvaluatingOrdinal = (1 << 30) - 1;
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// FUNCTION_ADDR(f) gets the address of a C function f.
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#define FUNCTION_ADDR(f) (reinterpret_cast<v8::internal::Address>(f))
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‎src/diagnostics/objects-debug.cc‎

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@@ -1519,7 +1519,7 @@ void SourceTextModule::SourceTextModuleVerify(Isolate* isolate) {
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}
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CHECK(!AsyncParentModuleCount());
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CHECK(!pending_async_dependencies());
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CHECK(!async_evaluating());
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CHECK(!IsAsyncEvaluating());
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}
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CHECK_EQ(requested_modules().length(), info().module_requests().length());

‎src/diagnostics/objects-printer.cc‎

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@@ -1746,6 +1746,7 @@ void SourceTextModule::SourceTextModulePrint(std::ostream& os) { // NOLINT
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os << "\n - requested_modules: " << Brief(requested_modules());
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os << "\n - import_meta: " << Brief(import_meta());
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os << "\n - cycle_root: " << Brief(cycle_root());
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os << "\n - async_evaluating_ordinal: " << async_evaluating_ordinal();
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os << "\n";
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}
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‎src/execution/isolate-inl.h‎

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@@ -14,6 +14,7 @@
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#include "src/objects/property-cell.h"
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#include "src/objects/regexp-match-info.h"
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#include "src/objects/shared-function-info.h"
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#include "src/objects/source-text-module-inl.h"
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namespace v8 {
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namespace internal {
@@ -120,6 +121,36 @@ bool Isolate::IsAnyInitialArrayPrototype(JSArray array) {
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return IsInAnyContext(array, Context::INITIAL_ARRAY_PROTOTYPE_INDEX);
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}
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void Isolate::DidFinishModuleAsyncEvaluation(unsigned ordinal) {
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// To address overflow, the ordinal is reset when the async module with the
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// largest vended ordinal finishes evaluating. Modules are evaluated in
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// ascending order of their async_evaluating_ordinal.
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//
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// While the specification imposes a global total ordering, the intention is
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// that for each async module, all its parents are totally ordered by when
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// they first had their [[AsyncEvaluating]] bit set.
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//
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// The module with largest vended ordinal finishes evaluating implies that the
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// async dependency as well as all other modules in that module's graph
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// depending on async dependencies are finished evaluating.
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//
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// If the async dependency participates in other module graphs (e.g. via
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// dynamic import, or other <script type=module> tags), those module graphs
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// must have been evaluated either before or after the async dependency is
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// settled, as the concrete Evaluate() method on cyclic module records is
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// neither reentrant nor performs microtask checkpoints during its
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// evaluation. If before, then all modules that depend on the async
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// dependencies were given an ordinal that ensure they are relatively ordered,
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// before the global ordinal was reset. If after, then the async evaluating
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// ordering does not apply, as the dependency is no longer asynchronous.
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//
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// https://tc39.es/ecma262/#sec-moduleevaluation
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if (ordinal + 1 == next_module_async_evaluating_ordinal_) {
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next_module_async_evaluating_ordinal_ =
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SourceTextModule::kFirstAsyncEvaluatingOrdinal;
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}
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}
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#define NATIVE_CONTEXT_FIELD_ACCESSOR(index, type, name) \
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Handle<type> Isolate::name() { \
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return Handle<type>(raw_native_context().name(), this); \

‎src/execution/isolate.cc‎

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@@ -74,6 +74,7 @@
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#include "src/objects/prototype.h"
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#include "src/objects/slots.h"
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#include "src/objects/smi.h"
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#include "src/objects/source-text-module-inl.h"
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#include "src/objects/stack-frame-info-inl.h"
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#include "src/objects/visitors.h"
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#include "src/profiler/heap-profiler.h"
@@ -2937,6 +2938,8 @@ Isolate::Isolate(std::unique_ptr<i::IsolateAllocator> isolate_allocator)
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#if V8_SFI_HAS_UNIQUE_ID
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next_unique_sfi_id_(0),
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#endif
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next_module_async_evaluating_ordinal_(
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SourceTextModule::kFirstAsyncEvaluatingOrdinal),
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cancelable_task_manager_(new CancelableTaskManager()) {
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TRACE_ISOLATE(constructor);
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CheckIsolateLayout();

‎src/execution/isolate.h‎

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@@ -1374,6 +1374,22 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
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return id;
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}
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// https://github.com/tc39/proposal-top-level-await/pull/159
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// TODO(syg): Update to actual spec link once merged.
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//
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// According to the spec, modules that depend on async modules (i.e. modules
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// with top-level await) must be evaluated in order in which their
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// [[AsyncEvaluating]] flags were set to true. V8 tracks this global total
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// order with next_module_async_evaluating_ordinal_. Each module that sets its
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// [[AsyncEvaluating]] to true grabs the next ordinal.
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unsigned NextModuleAsyncEvaluatingOrdinal() {
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unsigned ordinal = next_module_async_evaluating_ordinal_++;
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CHECK_LT(ordinal, kMaxModuleAsyncEvaluatingOrdinal);
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return ordinal;
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}
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inline void DidFinishModuleAsyncEvaluation(unsigned ordinal);
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void AddNearHeapLimitCallback(v8::NearHeapLimitCallback, void* data);
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void RemoveNearHeapLimitCallback(v8::NearHeapLimitCallback callback,
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size_t heap_limit);
@@ -1979,6 +1995,8 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
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std::atomic<int> next_unique_sfi_id_;
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#endif
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unsigned next_module_async_evaluating_ordinal_;
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// Vector of callbacks before a Call starts execution.
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std::vector<BeforeCallEnteredCallback> before_call_entered_callbacks_;
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‎src/heap/factory.cc‎

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@@ -2416,7 +2416,7 @@ Handle<SourceTextModule> Factory::NewSourceTextModule(
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module.set_dfs_ancestor_index(-1);
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module.set_flags(0);
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module.set_async(IsAsyncModule(sfi->kind()));
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module.set_async_evaluating(false);
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module.set_async_evaluating_ordinal(SourceTextModule::kNotAsyncEvaluated);
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module.set_cycle_root(roots.the_hole_value(), SKIP_WRITE_BARRIER);
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module.set_async_parent_modules(*async_parent_modules);
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module.set_pending_async_dependencies(0);

‎src/objects/module-inl.h‎

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Original file line numberDiff line numberDiff line change
@@ -38,8 +38,8 @@ SMI_ACCESSORS(Module, status, kStatusOffset)
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SMI_ACCESSORS(Module, hash, kHashOffset)
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BOOL_ACCESSORS(SourceTextModule, flags, async, AsyncBit::kShift)
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BOOL_ACCESSORS(SourceTextModule, flags, async_evaluating,
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AsyncEvaluatingBit::kShift)
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BIT_FIELD_ACCESSORS(SourceTextModule, flags, async_evaluating_ordinal,
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SourceTextModule::AsyncEvaluatingOrdinalBits)
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ACCESSORS(SourceTextModule, async_parent_modules, ArrayList,
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kAsyncParentModulesOffset)
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@@ -139,6 +139,10 @@ int SourceTextModule::AsyncParentModuleCount() {
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return async_parent_modules().Length();
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}
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bool SourceTextModule::IsAsyncEvaluating() const {
143+
return async_evaluating_ordinal() >= kFirstAsyncEvaluatingOrdinal;
144+
}
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bool SourceTextModule::HasPendingAsyncDependencies() {
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DCHECK_GE(pending_async_dependencies(), 0);
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return pending_async_dependencies() > 0;

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