1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef _NS_FONTCACHE_H_
#define _NS_FONTCACHE_H_
#include <stdint.h>
#include <sys/types.h>
#include "mozilla/RefPtr.h"
#include "nsCOMPtr.h"
#include "nsFontMetrics.h"
#include "nsIObserver.h"
#include "nsISupports.h"
#include "nsTArray.h"
#include "nsThreadUtils.h"
#include "prtime.h"
class gfxUserFontSet;
class nsAtom;
class nsPresContext;
struct nsFont;
class nsFontCache final : public nsIObserver {
public:
nsFontCache() : mContext(nullptr) {}
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIOBSERVER
void Init(nsPresContext* aContext);
void Destroy();
already_AddRefed<nsFontMetrics> GetMetricsFor(
const nsFont& aFont, const nsFontMetrics::Params& aParams);
void FontMetricsDeleted(const nsFontMetrics* aFontMetrics);
void Compact();
// Flush aFlushCount oldest entries, or all if aFlushCount is negative
void Flush(int32_t aFlushCount = -1);
void UpdateUserFonts(gfxUserFontSet* aUserFontSet);
protected:
// If the array of cached entries is about to exceed this threshold,
// we'll discard the oldest ones so as to keep the size reasonable.
// In practice, the great majority of cache hits are among the last
// few entries; keeping thousands of older entries becomes counter-
// productive because it can then take too long to scan the cache.
static constexpr int32_t kMaxCacheEntries = 128;
// Number of cache misses before we assume that a font fingerprinting attempt
// is being made. Usually fingerprinters will lookup the same font-family
// three times, as "sans-serif", "serif" and "monospace".
static constexpr int32_t kFingerprintingCacheMissThreshold = 3 * 20;
// We assume that fingerprinters will lookup a large number of fonts in a
// short amount of time.
static constexpr PRTime kFingerprintingTimeout =
PRTime(PR_USEC_PER_SEC) * 3; // 3 seconds
static_assert(kFingerprintingCacheMissThreshold < kMaxCacheEntries);
~nsFontCache() = default;
nsPresContext* mContext; // owner
RefPtr<nsAtom> mLocaleLanguage;
// We may not flush older entries immediately the array reaches
// kMaxCacheEntries length, because this usually happens on a stylo
// thread where we can't safely delete metrics objects. So we allocate an
// oversized autoarray buffer here, so that we're unlikely to overflow
// it and need separate heap allocation before the flush happens on the
// main thread.
AutoTArray<nsFontMetrics*, kMaxCacheEntries * 2> mFontMetrics;
bool mFlushPending = false;
class FlushFontMetricsTask : public mozilla::Runnable {
public:
explicit FlushFontMetricsTask(nsFontCache* aCache)
: mozilla::Runnable("FlushFontMetricsTask"), mCache(aCache) {}
NS_IMETHOD Run() override {
// Partially flush the cache, leaving the kMaxCacheEntries/2 most
// recent entries.
mCache->Flush(mCache->mFontMetrics.Length() - kMaxCacheEntries / 2);
mCache->mFlushPending = false;
return NS_OK;
}
private:
RefPtr<nsFontCache> mCache;
};
PRTime mLastCacheMiss = 0;
uint64_t mCacheMisses = 0;
bool mReportedProbableFingerprinting = false;
};
#endif /* _NS_FONTCACHE_H_ */
|
