src/Transients.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_TRANSIENTS_H
  10 #define SQUID_TRANSIENTS_H
  11
  12 #include "ipc/mem/Page.h"
  13 #include "ipc/mem/PageStack.h"
  14 #include "ipc/StoreMap.h"
  15 #include "Store.h"
  16 #include "store/Controlled.h"
  17 #include "store/forward.h"
  18 #include <vector>
  19
  20 typedef Ipc::StoreMap TransientsMap;
  21
  22 /// Keeps track of store entries being delivered to clients that arrived before
  23 /// those entries were [fully] cached. This SMP-shared table is necessary to
  24 /// * sync an entry-writing worker with entry-reading worker(s); and
  25 /// * sync an entry-deleting worker with both entry-reading/writing workers.
  26 class Transients: public Store::Controlled, public Ipc::StoreMapCleaner
  27 {
  28 public:
  29     /// shared entry metadata, used for synchronization
  30     class EntryStatus
  31     {
  32     public:
  33         bool abortedByWriter = false; ///< whether the entry was aborted
  34         bool waitingToBeFreed = false; ///< whether the entry was marked for deletion
  35         bool collapsed = false; ///< whether the entry allows collapsing
  36     };
  37
  38     Transients();
  39     virtual ~Transients();
  40
  41     /// return a local, previously collapsed entry
  42     StoreEntry *findCollapsed(const sfileno xitIndex);
  43
  44     /// removes collapsing requirement (for future hits)
  45     void clearCollapsingRequirement(const StoreEntry &e);
  46
  47     /// start listening for remote DELETE requests targeting either a complete
  48     /// StoreEntry (ioReading) or a being-formed miss StoreEntry (ioWriting)
  49     void monitorIo(StoreEntry*, const cache_key*, const Store::IoStatus);
  50
  51     /// called when the in-transit entry has been successfully cached
  52     void completeWriting(const StoreEntry &e);
  53
  54     /// copies current shared entry metadata into entryStatus
  55     void status(const StoreEntry &e, EntryStatus &entryStatus) const;
  56
  57     /// number of entry readers some time ago
  58     int readers(const StoreEntry &e) const;
  59
  60     /// the caller is done writing or reading the given entry
  61     void disconnect(StoreEntry &);
  62
  63     /* Store API */
  64     virtual StoreEntry *get(const cache_key *) override;
  65     virtual void create() override {}
  66     virtual void init() override;
  67     virtual uint64_t maxSize() const override;
  68     virtual uint64_t minSize() const override;
  69     virtual uint64_t currentSize() const override;
  70     virtual uint64_t currentCount() const override;
  71     virtual int64_t maxObjectSize() const override;
  72     virtual void getStats(StoreInfoStats &stats) const override;
  73     virtual void stat(StoreEntry &e) const override;
  74     virtual void reference(StoreEntry &e) override;
  75     virtual bool dereference(StoreEntry &e) override;
  76     virtual void evictCached(StoreEntry &) override;
  77     virtual void evictIfFound(const cache_key *) override;
  78     virtual void maintain() override;
  79
  80     /// Whether an entry with the given public key exists and (but) was
  81     /// marked for removal some time ago; get(key) returns nil in such cases.
  82     bool markedForDeletion(const cache_key *) const;
  83
  84     /// whether the entry is in "reading from Transients" I/O state
  85     bool isReader(const StoreEntry &) const;
  86     /// whether the entry is in "writing to Transients" I/O state
  87     bool isWriter(const StoreEntry &) const;
  88
  89     static int64_t EntryLimit();
  90
  91     /// Can we create and initialize Transients?
  92     static bool Enabled() { return EntryLimit(); }
  93
  94 protected:
  95     void addEntry(StoreEntry*, const cache_key *, const Store::IoStatus);
  96
  97     // Ipc::StoreMapCleaner API
  98     virtual void noteFreeMapSlice(const Ipc::StoreMapSliceId sliceId) override;
  99
 100 private:
 101     /// shared packed info indexed by Store keys, for creating new StoreEntries
 102     TransientsMap *map;
 103
 104     typedef std::vector<StoreEntry*> Locals;
 105     /// local collapsed reader and writer entries, indexed by transient ID,
 106     /// for syncing old StoreEntries
 107     Locals *locals;
 108 };
 109
 110 // TODO: Why use Store as a base? We are not really a cache.
 111
 112 #endif /* SQUID_TRANSIENTS_H */
 113