The prefs parser has two significant problems.
- It doesn't separate tokenizing from parsing.
- It is implemented as a loop around a big switch on a "current state"
variable.
As a result, it is hard to understand and modify, slower than it could be, and
in obscure cases (involving comments and whitespace) it fails to parse what
should be valid input.
This patch replaces it with a recursive descent parser (albeit one without any
recursion!) that has separate tokenization. The new parser is easier to
understand and modify, more correct, and has better error messages. It doesn't
do error recovery, but that would be much easier to add than in the old parser.
The new parser also runs about 1.9x faster than the existing parser. (As
measured by parsing greprefs.js's contents from memory 1000 times in
succession, omitting the prefs hash table construction. If the table
construction is included, it's about 1.6x faster.)
The new parser is slightly stricter than the old parser in a few ways.
- Disconcertingly, the old parser allowed arbitrary junk between prefs
(including at the start and end of the prefs file) so long as that junk
didn't include any of the following chars: '/', '#', 'u', 's', 'p'. I.e.
lines like these:
!foo@bar&pref("prefname", true);
ticky_pref("prefname", true); // missing 's' at start
User_pref("prefname", true); // should be 'u' at start
would all be treated the same as this:
pref("prefname", true);
The new parser disallows such junk because it isn't necessary and seems like
an unintentional botch by the old parser.
- The old parser allowed character 0x1a (SUB) between tokens and treated it
like '\n'.
The new parser does not allow this character. SUB was used to indicate
end-of-file (*not* end-of-line) in some old operating systems such as MS-DOS,
but this doesn't seem necessary today.
- The old parser tolerated (with a warning) invalid escape sequences within
string literals -- such as "\q" (not a valid escape) and "\x1" and "\u12"
(both of which have insufficient hex digits) -- accepting them literally.
The new parser does not tolerate invalid escape sequences because it doesn't
seem necessary and would complicate things.
- The old parser tolerated character 0x00 (NUL) within string literals; this is
dangerous because C++ code that manipulates string values with embedded NULs
will almost certainly consider those chars as end-of-string markers.
The new parser treats NUL chars as end-of-file, to avoid this danger and
because it facilitates a significant optimization (described within the
code).
- The old parser allowed integer literals to overflow, silently wrapping them.
The new parser treats integer overflow as a parse error. This seems better,
and it caught existing overflows of places.database.lastMaintenance, in
testing/profiles/prefs_general.js (bug 1424030) and
testing/talos/talos/config.py (bug 1434813).
The first of these changes meant that a couple of existing prefs with ";;" at
the end had to be changed (done in the preceding patch).
The minor increase in strictness shouldn't be a problem for default pref files
such as greprefs.js within the application (which we can modify), nor for
app-written prefs files such as prefs.js. It could affect user-written prefs
files such as user.js; the experience above suggests that integer overflow and
";;" are the most likely problems in practice. In my opinion, the risk here is
acceptable.
The new parser also does a better job of tracking line numbers because it (a)
treats "\r\n" sequences as a single end-of-line marker, and (a) pays attention
to end-of-line sequences within string literals.
Finally, the patch adds thorough tests of both valid and invalid syntax.
MozReview-Commit-ID: JD3beOQl4AJ
Bug 1383896 added this constant to testing/talos/talos/config.py:
> FAR_IN_FUTURE = 7258114800
which is used as the value for the "places.database.lastMaintenance" pref.
(7258114800 seconds after 1970 is the start of the year 2200.)
libpref stores integers prefs as int32_t and the current parser doesn't detect
overflow. So this overflows to -1331819792. (I detected this with the new prefs
parser from bug 1423840, which does detect integer overflow.) As a result the
condition testing this pref in
toolkit/components/places/PlacesCategoriesStarter.js ends up always succeeding
in tests, which is the exact opposite of what was intended. This patch changes
it to 2147483647 (the year 2038), the maximum int32_t value.
(Note: this is much the same as bug 1424030, which was fixed recently.)
MozReview-Commit-ID: AQw4b8tmE9u
CleanupFromTimeout is (transitively) recursing in calls to Close(), as that now leads to shutting down the plugin broker thread and CleanupFromTimeout was being rerun since nsThread::Shutdown runs tasks..
The Monitor's condition variable could be notified before the calling thread had begun to Wait for it. This caused the Notify to be missed, leading to hangs. By grabbing the Monitor in PostToDispatchHelper, we know Wait has been called because, otherwise, the calling thread would still hold the Monitor.
The prefs parser has two significant problems.
- It doesn't separate tokenizing from parsing.
- It is implemented as a loop around a big switch on a "current state"
variable.
As a result, it is hard to understand and modify, slower than it could be, and
in obscure cases (involving comments and whitespace) it fails to parse what
should be valid input.
This patch replaces it with a recursive descent parser (albeit one without any
recursion!) that has separate tokenization. The new parser is easier to
understand and modify, more correct, and has better error messages. It doesn't
do error recovery, but that would be much easier to add than in the old parser.
The new parser also runs about 1.9x faster than the existing parser. (As
measured by parsing greprefs.js's contents from memory 1000 times in
succession, omitting the prefs hash table construction. If the table
construction is included, it's about 1.6x faster.)
The new parser is slightly stricter than the old parser in a few ways.
- Disconcertingly, the old parser allowed arbitrary junk between prefs
(including at the start and end of the prefs file) so long as that junk
didn't include any of the following chars: '/', '#', 'u', 's', 'p'. I.e.
lines like these:
!foo@bar&pref("prefname", true);
ticky_pref("prefname", true); // missing 's' at start
User_pref("prefname", true); // should be 'u' at start
would all be treated the same as this:
pref("prefname", true);
The new parser disallows such junk because it isn't necessary and seems like
an unintentional botch by the old parser.
- The old parser allowed character 0x1a (SUB) between tokens and treated it
like '\n'.
The new parser does not allow this character. SUB was used to indicate
end-of-file (*not* end-of-line) in some old operating systems such as MS-DOS,
but this doesn't seem necessary today.
- The old parser tolerated (with a warning) invalid escape sequences within
string literals -- such as "\q" (not a valid escape) and "\x1" and "\u12"
(both of which have insufficient hex digits) -- accepting them literally.
The new parser does not tolerate invalid escape sequences because it doesn't
seem necessary and would complicate things.
- The old parser tolerated character 0x00 (NUL) within string literals; this is
dangerous because C++ code that manipulates string values with embedded NULs
will almost certainly consider those chars as end-of-string markers.
The new parser treats NUL chars as end-of-file, to avoid this danger and
because it facilitates a significant optimization (described within the
code).
- The old parser allowed integer literals to overflow, silently wrapping them.
The new parser treats integer overflow as a parse error. This seems better,
and it caught an existing overflow in testing/profiles/prefs_general.js, for
places.database.lastMaintenance (see bug 1424030).
The first of these changes meant that a couple of existing prefs with ";;" at
the end had to be changed (done in the preceding patch).
The minor increase in strictness shouldn't be a problem for default pref files
such as greprefs.js within the application (which we can modify), nor for
app-written prefs files such as prefs.js. It could affect user-written prefs
files such as user.js; the experience above suggests that ";;" is the most
likely problem in practice. In my opinion, the risk here is acceptable.
The new parser also does a better job of tracking line numbers because it (a)
treats "\r\n" sequences as a single end-of-line marker, and (a) pays attention
to end-of-line sequences within string literals.
Finally, the patch adds thorough tests of both valid and invalid syntax.
MozReview-Commit-ID: 8EYWH7KxGG
* * *
[mq]: win-fix
MozReview-Commit-ID: 91Bxjfghqfw
--HG--
extra : rebase_source : a8773413e5d68c33e4329df6819b6e1f82c22b85
This means we don't leave behind prefs-<n>.js files when prefs.js is read-only.
MozReview-Commit-ID: H6KKnoYGdhH
--HG--
extra : rebase_source : 263dd6fb75204a4565c8af89e7b21fc37a10d52e
Nicholas Nethercote
Liam Hodgins
Chris Pearce
Cosmin Sabou
Jeff Walden
David Parks
shindli
Felipe Gomes
Nathan Froyd
ffxbld
Andreas Pehrson
Andreea Pavel
Bogdan Tara
Julian Descottes
Dorel Luca
Dzmitry Malyshau
Coroiu Cristina
Sebastian Hengst
Mark Banner
Tom Prince
Joel Maher