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v8/test/cctest/test-weakmaps.cc
Jaroslav Sevcik a803fad068 Make sure the identity hash is uniform (at least in the lower bits). 
In the current implementation of hash code for objects (identity hash),
we do not bother to shift the hash when we retrieve it from the 
hash-length bitfield in a property array. (Even worse, we store shifted
value even if we do not have property array or inside dictionaries.)
That means that the hash-code for objects is always divisible by 1024.
Since our hash table uses a simple masking with (2^logsize - 1) to 
obtain the bucket, we get terrible hash collisions - essentially, our
hash table degenerates to a linked list for fewer than 1024 elements.

This CL always shifts the hash code so that the value in the lowest 
21 bits is uniformly distributed.

This results in big improvements on medium to large hash tables.
A program storing 1M elements into a WeakMap gets roughly
17x faster.  A program retrieving 1M elements from a Map 
improves even more dramatically (>100x).

const a = [];
for (let i = 0; i < 1e6; i++) a[i] = {};

const m = new Map();
console.time("Map.set");
for (let i = 0; i < 1e6; i++) {
  m.set(a[i], i);
}
console.timeEnd("Map.set");

console.time("Map.get");
let s = 0;
for (let i = 0; i < 1e6; i++) {
  s += m.get(a[i]);
}
console.timeEnd("Map.get");

const w = new WeakMap();
console.time("WeakMap.set");
for (let i = 0; i < 1e6; i++) {
  w.set(a[i], i);
}
console.timeEnd("WeakMap.set");

Before the fix:

Map.set: 157.575000
Map.get: 28333.182000
WeakMap.set: 6923.826000

After the fix:

Map.set: 178.382000
Map.get: 185.930000
WeakMap.set: 409.529000

Note that Map does not suffer from the hash collision on insertion because
it uses chaining (insertion into linked list is fast regardless of size!), and
we cleverly avoid lookup in the hash table on update if the key does not have 
identity hash yet. This is in contrast to the WeakMap, which uses 
open-addressing, and deals with collisions on insertion.

Bug: v8:6916
Change-Id: Ic5497bd4501e3b767b3f4acb7efb4784cbb3a2e4
Reviewed-on: https://chromium-review.googlesource.com/713616
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48480}
2017-10-12 03:47:56 +00:00

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// Copyright 2011 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include <utility>
#include "src/factory.h"
#include "src/global-handles.h"
#include "src/isolate.h"
#include "src/objects-inl.h"
#include "test/cctest/cctest.h"
#include "test/cctest/heap/heap-utils.h"
namespace v8 {
namespace internal {
namespace test_weakmaps {
static Isolate* GetIsolateFrom(LocalContext* context) {
return reinterpret_cast<Isolate*>((*context)->GetIsolate());
}
static Handle<JSWeakMap> AllocateJSWeakMap(Isolate* isolate) {
Handle<JSWeakMap> weakmap = isolate->factory()->NewJSWeakMap();
// Do not leak handles for the hash table, it would make entries strong.
{
HandleScope scope(isolate);
Handle<ObjectHashTable> table = ObjectHashTable::New(isolate, 1);
weakmap->set_table(*table);
}
return weakmap;
}
static int NumberOfWeakCalls = 0;
static void WeakPointerCallback(const v8::WeakCallbackInfo<void>& data) {
std::pair<v8::Persistent<v8::Value>*, int>* p =
reinterpret_cast<std::pair<v8::Persistent<v8::Value>*, int>*>(
data.GetParameter());
CHECK_EQ(1234, p->second);
NumberOfWeakCalls++;
p->first->Reset();
}
TEST(Weakness) {
FLAG_incremental_marking = false;
LocalContext context;
Isolate* isolate = GetIsolateFrom(&context);
Factory* factory = isolate->factory();
HandleScope scope(isolate);
Handle<JSWeakMap> weakmap = AllocateJSWeakMap(isolate);
GlobalHandles* global_handles = isolate->global_handles();
// Keep global reference to the key.
Handle<Object> key;
{
HandleScope scope(isolate);
Handle<Map> map = factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
Handle<JSObject> object = factory->NewJSObjectFromMap(map);
key = global_handles->Create(*object);
}
CHECK(!global_handles->IsWeak(key.location()));
// Put two chained entries into weak map.
{
HandleScope scope(isolate);
Handle<Map> map = factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
Handle<JSObject> object = factory->NewJSObjectFromMap(map);
Handle<Smi> smi(Smi::FromInt(23), isolate);
int32_t hash = key->GetOrCreateHash(isolate)->value();
JSWeakCollection::Set(weakmap, key, object, hash);
int32_t object_hash = object->GetOrCreateHash(isolate)->value();
JSWeakCollection::Set(weakmap, object, smi, object_hash);
}
CHECK_EQ(2, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
// Force a full GC.
CcTest::CollectAllGarbage(Heap::kAbortIncrementalMarkingMask);
CHECK_EQ(0, NumberOfWeakCalls);
CHECK_EQ(2, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
CHECK_EQ(
0, ObjectHashTable::cast(weakmap->table())->NumberOfDeletedElements());
// Make the global reference to the key weak.
std::pair<Handle<Object>*, int> handle_and_id(&key, 1234);
GlobalHandles::MakeWeak(
key.location(), reinterpret_cast<void*>(&handle_and_id),
&WeakPointerCallback, v8::WeakCallbackType::kParameter);
CHECK(global_handles->IsWeak(key.location()));
CcTest::CollectAllGarbage(Heap::kAbortIncrementalMarkingMask);
CHECK_EQ(1, NumberOfWeakCalls);
CHECK_EQ(0, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
CHECK_EQ(2,
ObjectHashTable::cast(weakmap->table())->NumberOfDeletedElements());
}
TEST(Shrinking) {
LocalContext context;
Isolate* isolate = GetIsolateFrom(&context);
Factory* factory = isolate->factory();
HandleScope scope(isolate);
Handle<JSWeakMap> weakmap = AllocateJSWeakMap(isolate);
// Check initial capacity.
CHECK_EQ(32, ObjectHashTable::cast(weakmap->table())->Capacity());
// Fill up weak map to trigger capacity change.
{
HandleScope scope(isolate);
Handle<Map> map = factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
for (int i = 0; i < 32; i++) {
Handle<JSObject> object = factory->NewJSObjectFromMap(map);
Handle<Smi> smi(Smi::FromInt(i), isolate);
int32_t object_hash = object->GetOrCreateHash(isolate)->value();
JSWeakCollection::Set(weakmap, object, smi, object_hash);
}
}
// Check increased capacity.
CHECK_EQ(128, ObjectHashTable::cast(weakmap->table())->Capacity());
// Force a full GC.
CHECK_EQ(32, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
CHECK_EQ(
0, ObjectHashTable::cast(weakmap->table())->NumberOfDeletedElements());
CcTest::CollectAllGarbage(Heap::kAbortIncrementalMarkingMask);
CHECK_EQ(0, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
CHECK_EQ(
32, ObjectHashTable::cast(weakmap->table())->NumberOfDeletedElements());
// Check shrunk capacity.
CHECK_EQ(32, ObjectHashTable::cast(weakmap->table())->Capacity());
}
// Test that weak map values on an evacuation candidate which are not reachable
// by other paths are correctly recorded in the slots buffer.
TEST(Regress2060a) {
if (i::FLAG_never_compact) return;
FLAG_always_compact = true;
LocalContext context;
Isolate* isolate = GetIsolateFrom(&context);
Factory* factory = isolate->factory();
Heap* heap = isolate->heap();
HandleScope scope(isolate);
Handle<JSFunction> function = factory->NewFunction(
factory->function_string());
Handle<JSObject> key = factory->NewJSObject(function);
Handle<JSWeakMap> weakmap = AllocateJSWeakMap(isolate);
// Start second old-space page so that values land on evacuation candidate.
Page* first_page = heap->old_space()->anchor()->next_page();
heap::SimulateFullSpace(heap->old_space());
// Fill up weak map with values on an evacuation candidate.
{
HandleScope scope(isolate);
for (int i = 0; i < 32; i++) {
Handle<JSObject> object = factory->NewJSObject(function, TENURED);
CHECK(!heap->InNewSpace(*object));
CHECK(!first_page->Contains(object->address()));
int32_t hash = key->GetOrCreateHash(isolate)->value();
JSWeakCollection::Set(weakmap, key, object, hash);
}
}
// Force compacting garbage collection.
CHECK(FLAG_always_compact);
CcTest::CollectAllGarbage();
}
// Test that weak map keys on an evacuation candidate which are reachable by
// other strong paths are correctly recorded in the slots buffer.
TEST(Regress2060b) {
if (i::FLAG_never_compact) return;
FLAG_always_compact = true;
#ifdef VERIFY_HEAP
FLAG_verify_heap = true;
#endif
LocalContext context;
Isolate* isolate = GetIsolateFrom(&context);
Factory* factory = isolate->factory();
Heap* heap = isolate->heap();
HandleScope scope(isolate);
Handle<JSFunction> function = factory->NewFunction(
factory->function_string());
// Start second old-space page so that keys land on evacuation candidate.
Page* first_page = heap->old_space()->anchor()->next_page();
heap::SimulateFullSpace(heap->old_space());
// Fill up weak map with keys on an evacuation candidate.
Handle<JSObject> keys[32];
for (int i = 0; i < 32; i++) {
keys[i] = factory->NewJSObject(function, TENURED);
CHECK(!heap->InNewSpace(*keys[i]));
CHECK(!first_page->Contains(keys[i]->address()));
}
Handle<JSWeakMap> weakmap = AllocateJSWeakMap(isolate);
for (int i = 0; i < 32; i++) {
Handle<Smi> smi(Smi::FromInt(i), isolate);
int32_t hash = keys[i]->GetOrCreateHash(isolate)->value();
JSWeakCollection::Set(weakmap, keys[i], smi, hash);
}
// Force compacting garbage collection. The subsequent collections are used
// to verify that key references were actually updated.
CHECK(FLAG_always_compact);
CcTest::CollectAllGarbage();
CcTest::CollectAllGarbage();
CcTest::CollectAllGarbage();
}
TEST(Regress399527) {
if (!FLAG_incremental_marking) return;
CcTest::InitializeVM();
v8::HandleScope scope(CcTest::isolate());
Isolate* isolate = CcTest::i_isolate();
Heap* heap = isolate->heap();
{
HandleScope scope(isolate);
AllocateJSWeakMap(isolate);
heap::SimulateIncrementalMarking(heap);
}
// The weak map is marked black here but leaving the handle scope will make
// the object unreachable. Aborting incremental marking will clear all the
// marking bits which makes the weak map garbage.
CcTest::CollectAllGarbage();
}
} // namespace test_weakmaps
} // namespace internal
} // namespace v8
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