src/ipc/mem/PagePool.h

   1 /*
   2  * Copyright (C) 1996-2020 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_MEM_PAGE_POOL_H
  10 #define SQUID_IPC_MEM_PAGE_POOL_H
  11
  12 #include "ipc/mem/Page.h"
  13 #include "ipc/mem/PageStack.h"
  14 #include "ipc/mem/Pointer.h"
  15
  16 namespace Ipc
  17 {
  18
  19 namespace Mem
  20 {
  21
  22 /// Atomic container of shared memory pages. Implemented using a collection of
  23 /// Segments, each with a PageStack index of free pages. All pools must be
  24 /// created by a single process.
  25 class PagePool
  26 {
  27 public:
  28     typedef Ipc::Mem::Owner<PageStack> Owner;
  29
  30     static Owner *Init(const char *const shmId, const Ipc::Mem::PoolId stackId, const unsigned int capacity, const size_t pageSize);
  31
  32     PagePool(const char *const id);
  33
  34     unsigned int capacity() const { return pageIndex->capacity(); }
  35     size_t pageSize() const { return pageIndex->pageSize(); }
  36     /// lower bound for the number of free pages
  37     unsigned int size() const { return pageIndex->size(); }
  38     /// approximate number of shared memory pages used now
  39     size_t level() const { return capacity() - size(); }
  40     /// approximate number of shared memory pages used now for given purpose
  41     size_t level(const int purpose) const;
  42
  43     /// sets page ID and returns true unless no free pages are found
  44     bool get(const PageId::Purpose purpose, PageId &page);
  45     /// makes identified page available as a free page to future get() callers
  46     void put(PageId &page);
  47     /// converts page handler into a temporary writeable shared memory pointer
  48     char *pagePointer(const PageId &page);
  49
  50 private:
  51     Ipc::Mem::Pointer<PageStack> pageIndex; ///< free pages index
  52     using Levels_t = PageStack::Levels_t;
  53
  54     /// number of shared memory pages used now for each purpose
  55     Levels_t * const theLevels;
  56     char *const theBuf; ///< pages storage
  57 };
  58
  59 } // namespace Mem
  60
  61 } // namespace Ipc
  62
  63 #endif // SQUID_IPC_MEM_PAGE_POOL_H
  64