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image/src/DiscardTracker.h@ac0c01689b40 (annotated)

image/src/DiscardTracker.h

Thu, 15 Jan 2015 15:59:08 +0100

author

Michael Schloh von Bennewitz <michael@schloh.com>

date

Thu, 15 Jan 2015 15:59:08 +0100

branch

TOR_BUG_9701

changeset 10

ac0c01689b40

permissions

-rw-r--r--

Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

michael@0	1	/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0	2	/* This Source Code Form is subject to the terms of the Mozilla Public
michael@0	3	* License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0	4	* You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0	5
michael@0	6	#ifndef mozilla_imagelib_DiscardTracker_h_
michael@0	7	#define mozilla_imagelib_DiscardTracker_h_
michael@0	8
michael@0	9	#include "mozilla/Atomics.h"
michael@0	10	#include "mozilla/LinkedList.h"
michael@0	11	#include "mozilla/Mutex.h"
michael@0	12	#include "mozilla/TimeStamp.h"
michael@0	13	#include "prlock.h"
michael@0	14	#include "nsThreadUtils.h"
michael@0	15	#include "nsAutoPtr.h"
michael@0	16
michael@0	17	class nsITimer;
michael@0	18
michael@0	19	namespace mozilla {
michael@0	20	namespace image {
michael@0	21
michael@0	22	class RasterImage;
michael@0	23
michael@0	24	/**
michael@0	25	* This static class maintains a linked list of RasterImage objects which are
michael@0	26	* eligible for discarding.
michael@0	27	*
michael@0	28	* When Reset() is called, the node is removed from its position in the list
michael@0	29	* (if it was there before) and appended to the beginnings of the list.
michael@0	30	*
michael@0	31	* Periodically (on a timer and when we notice that we're using more memory
michael@0	32	* than we'd like for decoded images), we go through the list and discard
michael@0	33	* decoded data from images at the end of the list.
michael@0	34	*/
michael@0	35	class DiscardTracker
michael@0	36	{
michael@0	37	public:
michael@0	38	/**
michael@0	39	* The DiscardTracker keeps a linked list of Node objects. Each object
michael@0	40	* points to a RasterImage and contains a timestamp indicating when the
michael@0	41	* node was inserted into the tracker.
michael@0	42	*
michael@0	43	* This structure is embedded within each RasterImage object, and we do
michael@0	44	* |mDiscardTrackerNode.img = this| on RasterImage construction. Thus, a
michael@0	45	* RasterImage must always call DiscardTracker::Remove() in its destructor
michael@0	46	* to avoid having the tracker point to bogus memory.
michael@0	47	*/
michael@0	48	struct Node : public LinkedListElement<Node>
michael@0	49	{
michael@0	50	RasterImage *img;
michael@0	51	TimeStamp timestamp;
michael@0	52	};
michael@0	53
michael@0	54	/**
michael@0	55	* Add an image to the front of the tracker's list, or move it to the front
michael@0	56	* if it's already in the list. This function is main thread only.
michael@0	57	*/
michael@0	58	static nsresult Reset(struct Node* node);
michael@0	59
michael@0	60	/**
michael@0	61	* Remove a node from the tracker; do nothing if the node is currently
michael@0	62	* untracked. This function is main thread only.
michael@0	63	*/
michael@0	64	static void Remove(struct Node* node);
michael@0	65
michael@0	66	/**
michael@0	67	* Initializes the discard tracker. This function is main thread only.
michael@0	68	*/
michael@0	69	static nsresult Initialize();
michael@0	70
michael@0	71	/**
michael@0	72	* Shut the discard tracker down. This should be called on XPCOM shutdown
michael@0	73	* so we destroy the discard timer's nsITimer. This function is main thread
michael@0	74	* only.
michael@0	75	*/
michael@0	76	static void Shutdown();
michael@0	77
michael@0	78	/**
michael@0	79	* Discard the decoded image data for all images tracked by the discard
michael@0	80	* tracker. This function is main thread only.
michael@0	81	*/
michael@0	82	static void DiscardAll();
michael@0	83
michael@0	84	/**
michael@0	85	* Inform the discard tracker that we are going to allocate some memory
michael@0	86	* for a decoded image. We use this to determine when we've allocated
michael@0	87	* too much memory and should discard some images. This function can be
michael@0	88	* called from any thread and is thread-safe. If this function succeeds, the
michael@0	89	* caller is now responsible for ensuring that InformDeallocation is called.
michael@0	90	*/
michael@0	91	static bool TryAllocation(uint64_t aBytes);
michael@0	92
michael@0	93	/**
michael@0	94	* Inform the discard tracker that we've deallocated some memory for a
michael@0	95	* decoded image. This function can be called from any thread and is
michael@0	96	* thread-safe.
michael@0	97	*/
michael@0	98	static void InformDeallocation(uint64_t aBytes);
michael@0	99
michael@0	100	private:
michael@0	101	/**
michael@0	102	* This is called when the discard timer fires; it calls into DiscardNow().
michael@0	103	*/
michael@0	104	friend void DiscardTimeoutChangedCallback(const char* aPref, void *aClosure);
michael@0	105
michael@0	106	/**
michael@0	107	* When run, this runnable sets sDiscardRunnablePending to false and calls
michael@0	108	* DiscardNow().
michael@0	109	*/
michael@0	110	class DiscardRunnable : public nsRunnable
michael@0	111	{
michael@0	112	NS_IMETHOD Run();
michael@0	113	};
michael@0	114
michael@0	115	static void ReloadTimeout();
michael@0	116	static nsresult EnableTimer();
michael@0	117	static void DisableTimer();
michael@0	118	static void MaybeDiscardSoon();
michael@0	119	static void TimerCallback(nsITimer *aTimer, void *aClosure);
michael@0	120	static void DiscardNow();
michael@0	121
michael@0	122	static LinkedList<Node> sDiscardableImages;
michael@0	123	static nsCOMPtr<nsITimer> sTimer;
michael@0	124	static bool sInitialized;
michael@0	125	static bool sTimerOn;
michael@0	126	static mozilla::Atomic<bool> sDiscardRunnablePending;
michael@0	127	static uint64_t sCurrentDecodedImageBytes;
michael@0	128	static uint32_t sMinDiscardTimeoutMs;
michael@0	129	static uint32_t sMaxDecodedImageKB;
michael@0	130	static uint32_t sHardLimitDecodedImageKB;
michael@0	131	// Lock for safegarding the 64-bit sCurrentDecodedImageBytes
michael@0	132	static PRLock *sAllocationLock;
michael@0	133	static mozilla::Mutex* sNodeListMutex;
michael@0	134	static Atomic<bool> sShutdown;
michael@0	135	};
michael@0	136
michael@0	137	} // namespace image
michael@0	138	} // namespace mozilla
michael@0	139
michael@0	140	#endif /* mozilla_imagelib_DiscardTracker_h_ */