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Add global caching, for /Resources without blend modes, and use it to reduce repeated fetching/parsing in PartialEvaluator.hasBlendModes

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The `PartialEvaluator.hasBlendModes` method is necessary to determine if there's any blend modes on a page, which unfortunately requires *synchronous* parsing of the /Resources of each page before its rendering can start (see the "StartRenderPage"-message).
In practice it's not uncommon for certain /Resources-entries to be found on more than one page (referenced via the XRef-table), which thus leads to unnecessary re-fetching/re-parsing of data in `PartialEvaluator.hasBlendModes`.

To improve performance, especially in pathological cases, we can cache /Resources-entries when it's absolutely clear that they do not contain *any* blend modes at all[1]. This way, subsequent `PartialEvaluator.hasBlendModes` calls can be made significantly more efficient.

This patch was tested using the PDF file from issue 6961, i.e. https://github.com/mozilla/pdf.js/files/121712/test.pdf:
```
[
    {  "id": "issue6961",
       "file": "../web/pdfs/issue6961.pdf",
       "md5": "a80e4357a8fda758d96c2c76f2980b03",
       "rounds": 100,
       "type": "eq"
    }
]
```

which gave the following results when comparing this patch against the `master` branch:
```
-- Grouped By browser, page, stat --
browser | page | stat         | Count | Baseline(ms) | Current(ms) |  +/- |     %  | Result(P<.05)
------- | ---- | ------------ | ----- | ------------ | ----------- | ---- | ------ | -------------
firefox | 0    | Overall      |   100 |         1034 |         555 | -480 | -46.39 |        faster
firefox | 0    | Page Request |   100 |          489 |           7 | -482 | -98.67 |        faster
firefox | 0    | Rendering    |   100 |          545 |         548 |    2 |   0.45 |
firefox | 1    | Overall      |   100 |          912 |         428 | -484 | -53.06 |        faster
firefox | 1    | Page Request |   100 |          487 |           1 | -486 | -99.77 |        faster
firefox | 1    | Rendering    |   100 |          425 |         427 |    2 |   0.51 |
```

---
[1] In the case where blend modes *are* found, it becomes a lot more difficult to know if it's generally safe to skip /Resources-entries. Hence we don't cache anything in that case, however note that most document/pages do not utilize blend modes anyway.
This commit is contained in:
Jonas Jenwald 2020-11-05 13:35:33 +01:00
parent 8b652d685b
commit 082cd8fc6c
4 changed files with 41 additions and 5 deletions
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22
src/core/primitives.js
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@ -277,8 +277,16 @@ var Ref = (function RefClosure() {
// The reference is identified by number and generation.
// This structure stores only one instance of the reference.
class RefSet {
constructor() {
this._set = new Set();
constructor(parent = null) {
if (
(typeof PDFJSDev === "undefined" ||
PDFJSDev.test("!PRODUCTION || TESTING")) &&
parent &&
!(parent instanceof RefSet)
) {
unreachable('RefSet: Invalid "parent" value.');
}
this._set = new Set(parent && parent._set);
}
has(ref) {
@ -292,6 +300,16 @@ class RefSet {
remove(ref) {
this._set.delete(ref.toString());
}
forEach(callback) {
for (const ref of this._set.values()) {
callback(ref);
}
}
clear() {
this._set.clear();
}
}
class RefSetCache {