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