最近最少使用cache，提取leveldb的lru cache部分，增加过期时间，过期失效

// 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. // // Endian-neutral encoding: // * Fixed-length numbers are encoded with least-significant byte first // * In addition we support variable length "varint" encoding // * Strings are encoded prefixed by their length in varint format #ifndef EXPIRELRU_CODING_H_ #define EXPIRELRU_CODING_H_ #include <stdint.h> #include <string.h> #include <string> #include "slice.h" #include "port_posix.h" namespace expirelru { // Standard Put... routines append to a string extern void PutFixed32(std::string* dst, uint32_t value); extern void PutFixed64(std::string* dst, uint64_t value); extern void PutVarint32(std::string* dst, uint32_t value); extern void PutVarint64(std::string* dst, uint64_t value); extern void PutLengthPrefixedSlice(std::string* dst, const Slice& value); // Standard Get... routines parse a value from the beginning of a Slice // and advance the slice past the parsed value. extern bool GetVarint32(Slice* input, uint32_t* value); extern bool GetVarint64(Slice* input, uint64_t* value); extern bool GetLengthPrefixedSlice(Slice* input, Slice* result); // Pointer-based variants of GetVarint... These either store a value // in *v and return a pointer just past the parsed value, or return // NULL on error. These routines only look at bytes in the range // [p..limit-1] extern const char* GetVarint32Ptr(const char* p,const char* limit, uint32_t* v); extern const char* GetVarint64Ptr(const char* p,const char* limit, uint64_t* v); // Returns the length of the varint32 or varint64 encoding of "v" extern int VarintLength(uint64_t v); // Lower-level versions of Put... that write directly into a character buffer // REQUIRES: dst has enough space for the value being written extern void EncodeFixed32(char* dst, uint32_t value); extern void EncodeFixed64(char* dst, uint64_t value); // Lower-level versions of Put... that write directly into a character buffer // and return a pointer just past the last byte written. // REQUIRES: dst has enough space for the value being written extern char* EncodeVarint32(char* dst, uint32_t value); extern char* EncodeVarint64(char* dst, uint64_t value); // Lower-level versions of Get... that read directly from a character buffer // without any bounds checking. inline uint32_t DecodeFixed32(const char* ptr) { if (port::kLittleEndian) { // Load the raw bytes uint32_t result; memcpy(&result, ptr, sizeof(result)); // gcc optimizes this to a plain load return result; } else { return ((static_cast<uint32_t>(static_cast<unsigned char>(ptr[0]))) | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[1])) << 8) | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[2])) << 16) | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[3])) << 24)); } } inline uint64_t DecodeFixed64(const char* ptr) { if (port::kLittleEndian) { // Load the raw bytes uint64_t result; memcpy(&result, ptr, sizeof(result)); // gcc optimizes this to a plain load return result; } else { uint64_t lo = DecodeFixed32(ptr); uint64_t hi = DecodeFixed32(ptr + 4); return (hi << 32) | lo; } } /* GetVarint32PtrFallback这个函数，仔细阅读这段代码，就能看出来， 这个函数是用于解析变长编码字符串的。先解码字符串首部的长度， 并且返回指向字符串真实地址的指针。 */ // Internal routine for use by fallback path of GetVarint32Ptr extern const char* GetVarint32PtrFallback(const char* p, const char* limit, uint32_t* value); inline const char* GetVarint32Ptr(const char* p, const char* limit, uint32_t* value) { if (p < limit) { uint32_t result = *(reinterpret_cast<const unsigned char*>(p)); if ((result & 128) == 0) { *value = result; return p + 1; } } return GetVarint32PtrFallback(p, limit, value); } } // namespace leveldb #endif // STORAGE_LEVELDB_UTIL_CODING_H_