src/ipc/MemMap.h

   1 /*
   2  * Copyright (C) 1996-2017 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef SQUID_IPC_STORE_MAP_H
  10 #define SQUID_IPC_STORE_MAP_H
  11
  12 #include "Debug.h"
  13 #include "ipc/mem/FlexibleArray.h"
  14 #include "ipc/mem/Pointer.h"
  15 #include "ipc/ReadWriteLock.h"
  16 #include "sbuf/SBuf.h"
  17 #include "store/forward.h"
  18 #include "store_key_md5.h"
  19 #include "tools.h"
  20
  21 #include <atomic>
  22
  23 namespace Ipc
  24 {
  25
  26 // The MEMMAP_SLOT_KEY_SIZE and MEMMAP_SLOT_DATA_SIZE must be enough big
  27 // to hold cached keys and data. Currently MemMap used only to store SSL
  28 // shared session data which have keys of 32bytes and at most 10K data
  29 #define MEMMAP_SLOT_KEY_SIZE 32
  30 #define MEMMAP_SLOT_DATA_SIZE 10*1024
  31
  32 /// a MemMap basic element, holding basic shareable memory block info
  33 class MemMapSlot
  34 {
  35 public:
  36     MemMapSlot();
  37     size_t size() const {return sizeof(MemMapSlot);}
  38     size_t keySize() const {return sizeof(key);}
  39     bool sameKey(const cache_key *const aKey) const;
  40     void set(const unsigned char *aKey, const void *block, size_t blockSize, time_t expire = 0);
  41     bool empty() const;
  42     bool reading() const { return lock.readers; }
  43     bool writing() const { return lock.writing; }
  44
  45     std::atomic<uint8_t> waitingToBeFreed; ///< may be accessed w/o a lock
  46     mutable ReadWriteLock lock; ///< protects slot data below
  47     unsigned char key[MEMMAP_SLOT_KEY_SIZE]; ///< The entry key
  48     unsigned char p[MEMMAP_SLOT_DATA_SIZE]; ///< The memory block;
  49     size_t pSize;
  50     time_t expire;
  51 };
  52
  53 class MemMapCleaner;
  54
  55 /// A map of MemMapSlots indexed by their keys, with read/write slot locking.
  56 class MemMap
  57 {
  58 public:
  59     typedef MemMapSlot Slot;
  60
  61     /// data shared across maps in different processes
  62     class Shared
  63     {
  64     public:
  65         Shared(const int aLimit, const size_t anExtrasSize);
  66         size_t sharedMemorySize() const;
  67         static size_t SharedMemorySize(const int limit, const size_t anExtrasSize);
  68         ~Shared();
  69
  70         const int limit; ///< maximum number of map slots
  71         const size_t extrasSize; ///< size of slot extra data
  72         std::atomic<int> count; ///< current number of map slots
  73         Ipc::Mem::FlexibleArray<Slot> slots; ///< storage
  74     };
  75
  76 public:
  77     typedef Mem::Owner<Shared> Owner;
  78
  79     /// initialize shared memory
  80     static Owner *Init(const char *const path, const int limit);
  81
  82     MemMap(const char *const aPath);
  83
  84     /// finds, locks and return a slot for an empty key position,
  85     /// erasing the old entry (if any)
  86     Slot *openForWriting(const cache_key *const key, sfileno &fileno);
  87
  88     /// locks and returns a slot for the empty fileno position; if
  89     /// overwriteExisting is false and the position is not empty, returns nil
  90     Slot *openForWritingAt(sfileno fileno, bool overwriteExisting = true);
  91
  92     /// successfully finish writing the entry
  93     void closeForWriting(const sfileno fileno, bool lockForReading = false);
  94
  95     /// only works on locked entries; returns nil unless the slot is readable
  96     const Slot *peekAtReader(const sfileno fileno) const;
  97
  98     /// mark the slot as waiting to be freed and, if possible, free it
  99     void free(const sfileno fileno);
 100
 101     /// open slot for reading, increments read level
 102     const Slot *openForReading(const cache_key *const key, sfileno &fileno);
 103
 104     /// open slot for reading, increments read level
 105     const Slot *openForReadingAt(const sfileno fileno);
 106
 107     /// close slot after reading, decrements read level
 108     void closeForReading(const sfileno fileno);
 109
 110     bool full() const; ///< there are no empty slots left
 111     bool valid(const int n) const; ///< whether n is a valid slot coordinate
 112     int entryCount() const; ///< number of used slots
 113     int entryLimit() const; ///< maximum number of slots that can be used
 114
 115     /// adds approximate current stats to the supplied ones
 116     void updateStats(ReadWriteLockStats &stats) const;
 117
 118     /// The cleaner MemMapCleaner::noteFreeMapSlot method called when a
 119     /// readable entry is freed.
 120     MemMapCleaner *cleaner;
 121
 122 protected:
 123     static Owner *Init(const char *const path, const int limit, const size_t extrasSize);
 124
 125     const SBuf path; ///< cache_dir path, used for logging
 126     Mem::Pointer<Shared> shared;
 127
 128 private:
 129     int slotIndexByKey(const cache_key *const key) const;
 130     Slot &slotByKey(const cache_key *const key);
 131
 132     Slot *openForReading(Slot &s);
 133     void abortWriting(const sfileno fileno);
 134     void freeIfNeeded(Slot &s);
 135     void freeLocked(Slot &s, bool keepLocked);
 136 };
 137
 138 /// API for adjusting external state when dirty map slot is being freed
 139 class MemMapCleaner
 140 {
 141 public:
 142     virtual ~MemMapCleaner() {}
 143
 144     /// adjust slot-linked state before a locked Readable slot is erased
 145     virtual void noteFreeMapSlot(const sfileno slotId) = 0;
 146 };
 147
 148 } // namespace Ipc
 149
 150 #endif /* SQUID_IPC_STORE_MAP_H */
 151