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368 righe
9.6 KiB
368 righe
9.6 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "db/skiplist.h"
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#include <atomic>
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#include <set>
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#include "gtest/gtest.h"
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#include "leveldb/env.h"
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#include "port/port.h"
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#include "port/thread_annotations.h"
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#include "util/arena.h"
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#include "util/hash.h"
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#include "util/random.h"
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#include "util/testutil.h"
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namespace leveldb {
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typedef uint64_t Key;
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struct Comparator {
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int operator()(const Key& a, const Key& b) const {
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if (a < b) {
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return -1;
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} else if (a > b) {
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return +1;
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} else {
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return 0;
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}
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}
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};
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TEST(SkipTest, Empty) {
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Arena arena;
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Comparator cmp;
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SkipList<Key, Comparator> list(cmp, &arena);
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ASSERT_TRUE(!list.Contains(10));
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SkipList<Key, Comparator>::Iterator iter(&list);
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ASSERT_TRUE(!iter.Valid());
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iter.SeekToFirst();
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ASSERT_TRUE(!iter.Valid());
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iter.Seek(100);
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ASSERT_TRUE(!iter.Valid());
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iter.SeekToLast();
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ASSERT_TRUE(!iter.Valid());
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}
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TEST(SkipTest, InsertAndLookup) {
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const int N = 2000;
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const int R = 5000;
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Random rnd(1000);
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std::set<Key> keys;
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Arena arena;
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Comparator cmp;
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SkipList<Key, Comparator> list(cmp, &arena);
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for (int i = 0; i < N; i++) {
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Key key = rnd.Next() % R;
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if (keys.insert(key).second) {
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list.Insert(key);
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}
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}
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for (int i = 0; i < R; i++) {
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if (list.Contains(i)) {
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ASSERT_EQ(keys.count(i), 1);
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} else {
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ASSERT_EQ(keys.count(i), 0);
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}
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}
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// Simple iterator tests
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{
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SkipList<Key, Comparator>::Iterator iter(&list);
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ASSERT_TRUE(!iter.Valid());
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iter.Seek(0);
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ASSERT_TRUE(iter.Valid());
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ASSERT_EQ(*(keys.begin()), iter.key());
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iter.SeekToFirst();
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ASSERT_TRUE(iter.Valid());
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ASSERT_EQ(*(keys.begin()), iter.key());
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iter.SeekToLast();
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ASSERT_TRUE(iter.Valid());
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ASSERT_EQ(*(keys.rbegin()), iter.key());
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}
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// Forward iteration test
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for (int i = 0; i < R; i++) {
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SkipList<Key, Comparator>::Iterator iter(&list);
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iter.Seek(i);
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// Compare against model iterator
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std::set<Key>::iterator model_iter = keys.lower_bound(i);
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for (int j = 0; j < 3; j++) {
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if (model_iter == keys.end()) {
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ASSERT_TRUE(!iter.Valid());
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break;
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} else {
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ASSERT_TRUE(iter.Valid());
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ASSERT_EQ(*model_iter, iter.key());
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++model_iter;
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iter.Next();
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}
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}
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}
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// Backward iteration test
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{
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SkipList<Key, Comparator>::Iterator iter(&list);
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iter.SeekToLast();
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// Compare against model iterator
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for (std::set<Key>::reverse_iterator model_iter = keys.rbegin();
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model_iter != keys.rend(); ++model_iter) {
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ASSERT_TRUE(iter.Valid());
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ASSERT_EQ(*model_iter, iter.key());
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iter.Prev();
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}
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ASSERT_TRUE(!iter.Valid());
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}
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}
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// We want to make sure that with a single writer and multiple
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// concurrent readers (with no synchronization other than when a
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// reader's iterator is created), the reader always observes all the
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// data that was present in the skip list when the iterator was
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// constructed. Because insertions are happening concurrently, we may
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// also observe new values that were inserted since the iterator was
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// constructed, but we should never miss any values that were present
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// at iterator construction time.
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//
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// We generate multi-part keys:
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// <key,gen,hash>
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// where:
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// key is in range [0..K-1]
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// gen is a generation number for key
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// hash is hash(key,gen)
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//
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// The insertion code picks a random key, sets gen to be 1 + the last
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// generation number inserted for that key, and sets hash to Hash(key,gen).
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//
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// At the beginning of a read, we snapshot the last inserted
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// generation number for each key. We then iterate, including random
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// calls to Next() and Seek(). For every key we encounter, we
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// check that it is either expected given the initial snapshot or has
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// been concurrently added since the iterator started.
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class ConcurrentTest {
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private:
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static constexpr uint32_t K = 4;
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static uint64_t key(Key key) { return (key >> 40); }
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static uint64_t gen(Key key) { return (key >> 8) & 0xffffffffu; }
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static uint64_t hash(Key key) { return key & 0xff; }
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static uint64_t HashNumbers(uint64_t k, uint64_t g) {
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uint64_t data[2] = {k, g};
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return Hash(reinterpret_cast<char*>(data), sizeof(data), 0);
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}
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static Key MakeKey(uint64_t k, uint64_t g) {
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static_assert(sizeof(Key) == sizeof(uint64_t), "");
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assert(k <= K); // We sometimes pass K to seek to the end of the skiplist
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assert(g <= 0xffffffffu);
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return ((k << 40) | (g << 8) | (HashNumbers(k, g) & 0xff));
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}
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static bool IsValidKey(Key k) {
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return hash(k) == (HashNumbers(key(k), gen(k)) & 0xff);
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}
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static Key RandomTarget(Random* rnd) {
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switch (rnd->Next() % 10) {
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case 0:
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// Seek to beginning
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return MakeKey(0, 0);
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case 1:
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// Seek to end
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return MakeKey(K, 0);
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default:
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// Seek to middle
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return MakeKey(rnd->Next() % K, 0);
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}
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}
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// Per-key generation
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struct State {
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std::atomic<int> generation[K];
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void Set(int k, int v) {
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generation[k].store(v, std::memory_order_release);
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}
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int Get(int k) { return generation[k].load(std::memory_order_acquire); }
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State() {
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for (int k = 0; k < K; k++) {
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Set(k, 0);
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}
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}
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};
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// Current state of the test
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State current_;
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Arena arena_;
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// SkipList is not protected by mu_. We just use a single writer
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// thread to modify it.
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SkipList<Key, Comparator> list_;
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public:
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ConcurrentTest() : list_(Comparator(), &arena_) {}
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// REQUIRES: External synchronization
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void WriteStep(Random* rnd) {
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const uint32_t k = rnd->Next() % K;
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const intptr_t g = current_.Get(k) + 1;
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const Key key = MakeKey(k, g);
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list_.Insert(key);
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current_.Set(k, g);
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}
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void ReadStep(Random* rnd) {
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// Remember the initial committed state of the skiplist.
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State initial_state;
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for (int k = 0; k < K; k++) {
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initial_state.Set(k, current_.Get(k));
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}
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Key pos = RandomTarget(rnd);
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SkipList<Key, Comparator>::Iterator iter(&list_);
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iter.Seek(pos);
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while (true) {
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Key current;
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if (!iter.Valid()) {
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current = MakeKey(K, 0);
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} else {
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current = iter.key();
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ASSERT_TRUE(IsValidKey(current)) << current;
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}
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ASSERT_LE(pos, current) << "should not go backwards";
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// Verify that everything in [pos,current) was not present in
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// initial_state.
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while (pos < current) {
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ASSERT_LT(key(pos), K) << pos;
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// Note that generation 0 is never inserted, so it is ok if
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// <*,0,*> is missing.
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ASSERT_TRUE((gen(pos) == 0) ||
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(gen(pos) > static_cast<Key>(initial_state.Get(key(pos)))))
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<< "key: " << key(pos) << "; gen: " << gen(pos)
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<< "; initgen: " << initial_state.Get(key(pos));
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// Advance to next key in the valid key space
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if (key(pos) < key(current)) {
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pos = MakeKey(key(pos) + 1, 0);
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} else {
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pos = MakeKey(key(pos), gen(pos) + 1);
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}
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}
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if (!iter.Valid()) {
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break;
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}
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if (rnd->Next() % 2) {
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iter.Next();
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pos = MakeKey(key(pos), gen(pos) + 1);
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} else {
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Key new_target = RandomTarget(rnd);
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if (new_target > pos) {
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pos = new_target;
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iter.Seek(new_target);
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}
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}
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}
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}
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};
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// Needed when building in C++11 mode.
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constexpr uint32_t ConcurrentTest::K;
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// Simple test that does single-threaded testing of the ConcurrentTest
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// scaffolding.
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TEST(SkipTest, ConcurrentWithoutThreads) {
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ConcurrentTest test;
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Random rnd(test::RandomSeed());
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for (int i = 0; i < 10000; i++) {
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test.ReadStep(&rnd);
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test.WriteStep(&rnd);
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}
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}
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class TestState {
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public:
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ConcurrentTest t_;
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int seed_;
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std::atomic<bool> quit_flag_;
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enum ReaderState { STARTING, RUNNING, DONE };
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explicit TestState(int s)
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: seed_(s), quit_flag_(false), state_(STARTING), state_cv_(&mu_) {}
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void Wait(ReaderState s) LOCKS_EXCLUDED(mu_) {
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mu_.Lock();
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while (state_ != s) {
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state_cv_.Wait();
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}
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mu_.Unlock();
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}
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void Change(ReaderState s) LOCKS_EXCLUDED(mu_) {
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mu_.Lock();
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state_ = s;
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state_cv_.Signal();
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mu_.Unlock();
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}
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private:
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port::Mutex mu_;
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ReaderState state_ GUARDED_BY(mu_);
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port::CondVar state_cv_ GUARDED_BY(mu_);
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};
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static void ConcurrentReader(void* arg) {
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TestState* state = reinterpret_cast<TestState*>(arg);
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Random rnd(state->seed_);
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int64_t reads = 0;
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state->Change(TestState::RUNNING);
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while (!state->quit_flag_.load(std::memory_order_acquire)) {
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state->t_.ReadStep(&rnd);
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++reads;
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}
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state->Change(TestState::DONE);
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}
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static void RunConcurrent(int run) {
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const int seed = test::RandomSeed() + (run * 100);
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Random rnd(seed);
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const int N = 1000;
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const int kSize = 1000;
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for (int i = 0; i < N; i++) {
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if ((i % 100) == 0) {
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std::fprintf(stderr, "Run %d of %d\n", i, N);
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}
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TestState state(seed + 1);
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Env::Default()->Schedule(ConcurrentReader, &state);
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state.Wait(TestState::RUNNING);
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for (int i = 0; i < kSize; i++) {
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state.t_.WriteStep(&rnd);
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}
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state.quit_flag_.store(true, std::memory_order_release);
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state.Wait(TestState::DONE);
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}
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}
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TEST(SkipTest, Concurrent1) { RunConcurrent(1); }
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TEST(SkipTest, Concurrent2) { RunConcurrent(2); }
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TEST(SkipTest, Concurrent3) { RunConcurrent(3); }
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TEST(SkipTest, Concurrent4) { RunConcurrent(4); }
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TEST(SkipTest, Concurrent5) { RunConcurrent(5); }
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} // namespace leveldb
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