For reasons unknown, if you give MSVC:
// Foo.h
struct Foo
{
...
};
extern const Foo gFoo;
// Foo.cpp, which necessarily includes Foo.h.
extern constexpr Foo gFoo = {
};
MSVC will create a static initializer for gFoo and place it in the
read/write data section, rather than the read-only data section.
Removing the `extern const` declaration seems to be enough to make this
problem go away. We need to adjust the declaration of other variables
to compensate for the non-visibility of gFoo in the header file.
Each nsStaticAtomSetup contains a pointer to a static atom, and also a pointer
to the canonical pointer to that static atom. Which is pretty weird! The
notable thing thing about it is that these structs are in an array, and that
gives us the only way to iterate over all static atoms in a single class, for
registration and lookups.
But thanks to various other recent changes to the implementation of static
atoms, we can now put the static atoms themselves into an array, which can be
iterated over. So this patch does that. With that done, nsStaticAtomSetup is no
longer necessary.
According to the `size` utility, on Linux64 this reduces the size of libxul.so
by the following amounts:
> text: 62008 bytes
> data: 20992 bytes
> bss: 21040 bytes
> total: 104040 bytes
- The bss reduction is one word per atom, because the canonical static atom
pointers (e.g. nsGkAtoms::foo) have moved from .bss to .data, because they're
now initialized at compile time instead of runtime.
- The data reduction is one word per atom, because we remove two words per atom
for the nsStaticAtomSetup removal, but gain one word per atom from the
previous bullet point.
- I'm not sure about the text reduction. It's three words per atom. Maybe
because there is one less relocation per atom?
Other notable things in the patch:
- nsICSSAnonBoxPseudo and nsICSSPseudoElement now inherit from nsStaticAtom,
not nsAtom, because that's more precise.
- Each static atoms array now has an enum associated with it, which is used in
various ways.
- In the big comment about the macros at the top of nsStaticAtom.h, the pre-
and post-expansion forms are now shown interleaved. The interleaving reduces
duplication and makes the comment much easier to read and maintain. The
comment also has an introduction that explains the constraints and goals of
the implementation.
- The SUBCLASS macro variations are gone. There are few enough users of these
macros now that always passing the atom type has become simpler.
MozReview-Commit-ID: 1GmfKidLjaU
--HG--
extra : rebase_source : 2352590101fc6693ba388f885ca4714a42963943
For nsCSSAnonBoxes.cpp, nsCSSPseudoElements.cpp, nsDirectoryService.cpp, the
corresponding .h file includes nsStaticAtom.h. For the other files in this
patch, nsStaticAtom.h is not needed at all.
MozReview-Commit-ID: IpMmbXwZHhu
--HG--
extra : rebase_source : 46d0a6b40a41ee233adad7c205cf907fa27de34a
On Windows there are some duplicate keys in nsDirectoryService:
- NS_WIN_STARTUP_DIR is "Strt", and maps to Win_Startup.
- NS_WIN_STARTMENU_DIR is also "Strt", and is meant to map to Win_Startmenu,
but actually maps to Win_Startup because of the key duplication.
- NS_WIN_COMMON_STARTMENU_DIR is "CmStrt", and maps to Win_Common_Startmenu.
- NS_WIN_COMMON_STARTUP_DIR is also "CmStrt", and is meant to map to
Win_Common_Startup, but actually maps to Win_Common_Startmenu because of
the key duplication.
Given the bugginess, it's unsurprising that they aren't used.
This patch removes them. This gets rid of two duplicate static atoms, helping
with bug 1445113.
MozReview-Commit-ID: 9Yx6M0VUaH4
--HG--
extra : rebase_source : 887cb2f2b907a6f3a7b796b6032b385291862323
Currently static atoms are stored on the heap, but their char buffers are
stored in read-only static memory.
This patch changes the representation of nsStaticAtom (thus making it a
non-trivial subclass of nsAtom). Instead of a pointer to the string, it now has
an mStringOffset field which is a 32-bit offset to the string. (This requires
placement of the string and the atom within the same object so that the offset
is known to be small. The docs and macros in nsStaticAtom.h handle that.)
Static and dynamic atoms now store their chars in different ways: nsStaticAtom
stores them inline, nsDynamicAtom has a pointer to separate storage. So
`mString` and GetStringBuffer() move from nsAtom to nsDynamicAtom.
The change to static atoms means they can be made constexpr and stored in
read-only memory instead of on the heap. On 64-bit this reduces the per-process
overhead by 16 bytes; on 32-bit the saving is 12 bytes. (Further reductions
will be possible in follow-up patches.)
The increased use of constexpr required multiple workarounds for MSVC.
- Multiple uses of MOZ_{PUSH,POP}_DISABLE_INTEGRAL_CONSTANT_OVERFLOW_WARNING to
disable warnings about (well-defined!) overflow of unsigned integer
arithmetic.
- The use of -Zc:externConstexpr on all files defining static atoms, to make
MSVC follow the C++ standard(!) and let constexpr variables have external
linkage.
- The use of -constexpr:steps300000 to increase the number of operations
allowed in a constexpr value, in order to handle gGkAtoms, which requires
hashing ~2,500 atom strings.
The patch also changes how HTML5 atoms are handled. They are now treated as
dynamic atoms, i.e. we have "dynamic normal" atoms and "dynamic HTML5 atoms",
and "dynamic atoms" covers both cases, and both are represented via
nsDynamicAtom. The main difference between the two kinds is that dynamic HTML5
atoms still aren't allowed to be used in various operations, most notably
AddRef()/Release(). All this also required moving nsDynamicAtom into the header
file.
There is a slight performance cost to all these changes: now that nsStaticAtom
and nsDynamicAtom store their chars in different ways, a conditional branch is
required in the following functions: Equals(), GetUTF16String(),
WeakAtom::as_slice().
Finally, in about:memory the "explicit/atoms/static/atom-objects" value is no
longer needed, because that memory is static instead of heap-allocated.
MozReview-Commit-ID: 4AxPv05ngZy
nsGkAtoms::Home and nsDirectoryAtoms::sOS_HomeDirectory are duplicate static
atoms. This patch comments out the latter to remove the duplication.
MozReview-Commit-ID: LGkjZn0zaoz
There are ways for Create() to return access denied for files which already
exist, particularly in the case of locked files. When it does, createUnique()
should check whether the file exists before considering the attempt a failure.
MozReview-Commit-ID: FyJTghk04jH
--HG--
extra : rebase_source : 10e6f2cb7da18e8e6d410b52a593b7455f0d76fa
The intention is a little more clear with static_assert, as well as
failing sooner. (The code is probably the same, since the compiler will
optimize out the checks as dead code, but meh.)
Reading nsIIDs to binary streams requires 1 + 1 + 1 + 8 calls to Read
for the underlying stream. With the assumption that reading to the
underlying stream for a binary stream is relatively expensive, we should
be able to do better by reading the byte array in an nsIID in a single
Read() request. The same logic applies to writing nsIIDs. Performing a
single operation here should not change the actual bytes read or
written. Performing a single operation also has the virtue of
performing fewer error checks and whatnot.
This adds a fallible version of |NS_UnescapeURL| that can be used to
gracefully handle allocation failures when the string needs to be unescaped.
--HG--
extra : rebase_source : 8d10ca98fb372afe8219d744b147703254e02830
This method is used to replace some GetNativePath usage for logging.
MozReview-Commit-ID: 9nWf2r4oviA
--HG--
extra : rebase_source : b58e45ab38621179cd802979131fdddbfe65079e
extra : intermediate-source : b4ded2247082f98fe18eb640c5fafeb9bc107ac0
extra : source : 21a82c1faeffc7c0d7b3a5ef0ae4c5243c81a586
This method is used by some subsequent patches when unique opaque identifiers are necessary.
MozReview-Commit-ID: AreqK4MHdJP
--HG--
extra : rebase_source : d5b85c2c9212618f54a6ac2f5199651b01c99510
extra : intermediate-source : 67c3c7a1012b9fdd628928bec61472c6ce580616
extra : source : c9a67330c600dbe454fd2ce5025247171e0c0e22
Currently only |value_type| is implemented.
MozReview-Commit-ID: 1mejzvkuako
--HG--
extra : rebase_source : 69e08073adbb9a866db26e515702a0659ece0a70
extra : intermediate-source : 3696381ddfdc19ab2f901ca4247e1cb4efb27731
extra : source : 35d760da1d73dd51614f434c26e5ce80ff690829
Nathan Froyd
Andrea Marchesini
Sebastian Hengst
Tristan Bourvon
Nicholas Nethercote
Henri Sivonen
Andreea Pavel
Kris Maglione
Jeff Walden
Masatoshi Kimura
Eric Rahm
Alex Gaynor
Gian-Carlo Pascutto
Chris Peterson
Swapnil
Valentin Gosu
Philippe Normand
Sylvestre Ledru
Cosmin Sabou