Revision 0d4a2b733070a1bd52f981313f9e17f126701407 authored by Yi Wu on 04 August 2017, 20:09:56 UTC, committed by Facebook Github Bot on 04 August 2017, 20:12:07 UTC
Summary: The FsyncFiles background job call Fsync() periodically for blob files. However it can access WritableFileWriter concurrently with a Put() or Write(). And WritableFileWriter does not support concurrent access. It will lead to WritableFileWriter buffer being flush with same content twice, and blob file end up corrupted. Fixing by simply let FsyncFiles hold write_mutex_. Closes https://github.com/facebook/rocksdb/pull/2685 Differential Revision: D5561908 Pulled By: yiwu-arbug fbshipit-source-id: f0bb5bcab0e05694e053b8c49eab43640721e872
1 parent 627c9f1
random.h
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// 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.
#pragma once
#include <random>
#include <stdint.h>
namespace rocksdb {
// A very simple random number generator. Not especially good at
// generating truly random bits, but good enough for our needs in this
// package.
class Random {
private:
enum : uint32_t {
M = 2147483647L // 2^31-1
};
enum : uint64_t {
A = 16807 // bits 14, 8, 7, 5, 2, 1, 0
};
uint32_t seed_;
static uint32_t GoodSeed(uint32_t s) { return (s & M) != 0 ? (s & M) : 1; }
public:
// This is the largest value that can be returned from Next()
enum : uint32_t { kMaxNext = M };
explicit Random(uint32_t s) : seed_(GoodSeed(s)) {}
void Reset(uint32_t s) { seed_ = GoodSeed(s); }
uint32_t Next() {
// We are computing
// seed_ = (seed_ * A) % M, where M = 2^31-1
//
// seed_ must not be zero or M, or else all subsequent computed values
// will be zero or M respectively. For all other values, seed_ will end
// up cycling through every number in [1,M-1]
uint64_t product = seed_ * A;
// Compute (product % M) using the fact that ((x << 31) % M) == x.
seed_ = static_cast<uint32_t>((product >> 31) + (product & M));
// The first reduction may overflow by 1 bit, so we may need to
// repeat. mod == M is not possible; using > allows the faster
// sign-bit-based test.
if (seed_ > M) {
seed_ -= M;
}
return seed_;
}
// Returns a uniformly distributed value in the range [0..n-1]
// REQUIRES: n > 0
uint32_t Uniform(int n) { return Next() % n; }
// Randomly returns true ~"1/n" of the time, and false otherwise.
// REQUIRES: n > 0
bool OneIn(int n) { return (Next() % n) == 0; }
// Skewed: pick "base" uniformly from range [0,max_log] and then
// return "base" random bits. The effect is to pick a number in the
// range [0,2^max_log-1] with exponential bias towards smaller numbers.
uint32_t Skewed(int max_log) {
return Uniform(1 << Uniform(max_log + 1));
}
// Returns a Random instance for use by the current thread without
// additional locking
static Random* GetTLSInstance();
};
// A simple 64bit random number generator based on std::mt19937_64
class Random64 {
private:
std::mt19937_64 generator_;
public:
explicit Random64(uint64_t s) : generator_(s) { }
// Generates the next random number
uint64_t Next() { return generator_(); }
// Returns a uniformly distributed value in the range [0..n-1]
// REQUIRES: n > 0
uint64_t Uniform(uint64_t n) {
return std::uniform_int_distribution<uint64_t>(0, n - 1)(generator_);
}
// Randomly returns true ~"1/n" of the time, and false otherwise.
// REQUIRES: n > 0
bool OneIn(uint64_t n) { return Uniform(n) == 0; }
// Skewed: pick "base" uniformly from range [0,max_log] and then
// return "base" random bits. The effect is to pick a number in the
// range [0,2^max_log-1] with exponential bias towards smaller numbers.
uint64_t Skewed(int max_log) {
return Uniform(uint64_t(1) << Uniform(max_log + 1));
}
};
} // namespace rocksdb
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