gecko/modules/libpr0n/src/DiscardTracker.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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 *   Bobby Holley <bobbyholley@gmail.com>
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#ifndef mozilla_imagelib_DiscardTracker_h_
#define mozilla_imagelib_DiscardTracker_h_

#define DISCARD_TIMEOUT_PREF "image.mem.min_discard_timeout_ms"

class nsITimer;

namespace mozilla {
namespace imagelib {
class RasterImage;

// Struct to make a RasterImage insertable into the tracker list. This
// is embedded within each RasterImage object, and we do 'this->curr = this'
// on RasterImage construction. Thus, a RasterImage must always call
// DiscardTracker::Remove() in its destructor to avoid having the tracker
// point to bogus memory.
struct DiscardTrackerNode
{
  // Pointer to the RasterImage that this node tracks
  RasterImage *curr;

  // Pointers to the previous and next nodes in the list
  DiscardTrackerNode *prev, *next;
};

/**
 * This static class maintains a linked list of RasterImage nodes. When Reset()
 * is called, the node is removed from its position in the list (if it was there
 * before) and appended to the end. When Remove() is called, the node is removed
 * from the list. The timer fires once every MIN_DISCARD_TIMEOUT_MS ms. When it
 * does, it calls Discard() on each container preceding it, and then appends
 * itself to the end of the list. Thus, the discard timeout varies between
 * MIN_DISCARD_TIMEOUT_MS and 2*MIN_DISCARD_TIMEOUT_MS.
 */
class DiscardTracker
{
  public:
    static nsresult Reset(struct DiscardTrackerNode *node);
    static void Remove(struct DiscardTrackerNode *node);
    static void Shutdown();
    static void ReloadTimeout();
  private:
    static nsresult Initialize();
    static nsresult TimerOn();
    static void TimerOff();
    static void TimerCallback(nsITimer *aTimer, void *aClosure);
};

} // namespace imagelib
} // namespace mozilla

#endif /* mozilla_imagelib_DiscardTracker_h_ */