src/ipc/mem/PagePool.h

   1 /*
   2  * $Id$
   3  *
   4  */
   5
   6 #ifndef SQUID_IPC_MEM_PAGE_POOL_H
   7 #define SQUID_IPC_MEM_PAGE_POOL_H
   8
   9 #include "ipc/mem/PageStack.h"
  10 #include "ipc/mem/Segment.h"
  11
  12 namespace Ipc {
  13
  14 namespace Mem {
  15
  16 class PageId;
  17
  18 /// Atomic container of shared memory pages. Implemented using a collection of
  19 /// Segments, each with a PageStack index of free pages. All pools must be
  20 /// created by a single process.
  21 class PagePool {
  22 public:
  23     /// creates a new shared page pool that can hold up to capacity pages of pageSize size
  24     PagePool(const String &id, const unsigned int capacity, const size_t pageSize);
  25     /// attaches to the identified shared page pool
  26     PagePool(const String &id);
  27     /// unlinks shared memory segments
  28     static void Unlink(const String &id);
  29
  30     unsigned int capacity() const { return shared->theCapacity; }
  31     /// lower bound for the number of free pages
  32     unsigned int size() const { return pageIndex.size(); }
  33     size_t pageSize() const { return shared->thePageSize; }
  34
  35     /// sets page ID and returns true unless no free pages are found
  36     bool get(PageId &page);
  37     /// makes identified page available as a free page to future get() callers
  38     void put(PageId &page);
  39     /// converts page handler into a temporary writeable shared memory pointer
  40     void *pagePointer(const PageId &page);
  41
  42 private:
  43     inline bool pageIdIsValid(const PageId &page) const;
  44
  45     struct Shared {
  46         Shared(const unsigned int aCapacity, const size_t aPageSize);
  47
  48         /// total shared memory size required to share
  49         static off_t MemSize(const unsigned int capacity, const size_t pageSize);
  50
  51         const unsigned int theId; ///< pool id
  52         const unsigned int theCapacity; ///< number of pages in the pool
  53         const size_t thePageSize; ///< page size
  54
  55         // TODO: add padding to make pages system page-aligned?
  56         char theBuf[]; ///< pages storage
  57     };
  58
  59     PageStack pageIndex; ///< free pages index
  60     Segment shm; ///< shared memory segment to store metadata (and pages)
  61     Shared *shared; ///< our metadata and page storage, shared among all pool users
  62 };
  63
  64 } // namespace Mem
  65
  66 } // namespace Ipc
  67
  68 #endif // SQUID_IPC_MEM_PAGE_POOL_H