vdbgln() was responsible for ~10% of samples on pv's flamegraph for
RequestServer (under request_did_finish) when loading github.com in
Browser and recording a whole-system profile. This makes that almost
completely disappear.
BigEndianInputBitStream is the Core::Stream API's bitwise input stream
for big endian input data. The functionality and bitwise read API is
almost unchanged from AK::BitStream, except that this bit stream only
supports big endian operations.
As the behavior for mixing big endian and little endian reads on
AK::BitStream is unknown (and untested), it was never done anyways. So
this was a good opportunity to split up big endian and little endian
reading.
Another API improvement from AK::BitStream is the ability to specify
the return type of the bit read function. Always needing to static_cast
the result of BitStream::read_bits_big_endian into the desired type is
adding a lot of avoidable noise to the users (primarily FlacLoader).
Regardless of the backing type that the number would otherwise parse to,
if it is zero and the sign was supposed to be negative then it needs to
be a floating point number to represent the correct value.
This implements an 8-bit front stencil buffer. Stencil operations are
SIMD optimized. LibGL changes include:
* New `glStencilMask` and `glStencilMaskSeparate` functions
* New context parameter `GL_STENCIL_CLEAR_VALUE`
In this particular case, auto is a footgun, because we are very
certain about the type that we want to return. const-correctness
could have been violated (as Vector did), because Iterator did not
enforce that the returned pointer was actually const if the Iterator
was an Iterator over a const container.
Methods marked as const should always only return Foo const&, never
Foo&. Previously, this only worked correctly with Foo, but not with
Foo&: If someone fetched a T const&, this would have been expanded
to Foo& const& which is just Foo&. Therefore, they were able to modify
the elements of the Vector, even though it was marked as const.
This commit fixes that by introducing VisibleType as an alias for
RemoveReference<T> and using it throughout Vector.
There are also other cases where we don't require a mutable reference
to the underlying type, only a const reference (for example in a find
operation). In these cases, we now also correctly expand the type
to Foo const&.
This is particularly useful in the Kernel, where the physical pages of
a VMObject are stored as a FixedArray but often passed around as a Span
from which a new FixedArray should be cloned.
This makes the following code behave as expected:
Variant<int, String> x { some_string() };
x.visit(
[](String const&) {}, // Expectation is for this to be called
[](auto&) {});
This is useful for writing new data at the end of a ByteBuffer. For
instance, with the Stream API:
auto pending_bytes = TRY(stream.pending_bytes());
auto receive_buffer = TRY(buffer.get_bytes_for_writing(
pending_bytes));
TRY(stream.read(receive_buffer));
Except for tangential accessors such as data(), there is no more feature
of FixedArray that is untested after this large expansion of its test
cases. These tests, with the help of the new NoAllocationGuard, also
test the allocation contract that was fixated in the last commit.
Hopefully this builds confidence in future Kernel uses of FixedArray
as well as its establishment in the real-time parts of the audio
subsystem. I'm excited :^)
FixedArray always *almost* had the following allocation guarantees:
There is (possibly) one allocation in the constructor and one (or more)
deallocation(s) in the destructor. No other operation allocates or
deallocates. With this removal of the public clear() method, which
nobody except the test used anyways, those guarantees are now completely
true and furthermore fixated with an explanatory comment.
Because we don't have our LibC on Lagom, the allocation guard global
flag doesn't exist and NoAllocationGuard fails to build on Lagom.
Whoops. For now, just disable NoAllocationGuard's functionality here.
StringView::for_each_split_view allows you to process the splits in a
StringView without needing to allocate a Vector<StringView> to store
each of the parts.
Since we migrated the implementation from the normal split_view path, we
can also re-implement split_view in terms of for_each_split_view.
This mechanism was unsafe to use in any multithreaded context, since
the hook function was invoked on a raw pointer *after* decrementing
the local ref count.
Since we don't use it for anything anymore, let's just get rid of it.
Currently, we define a CaseInsensitiveStringTraits structure for String.
Using this structure for StringView involves allocating a String from
that view, and a second string to convert that intermediate string to
lowercase.
This defines CaseInsensitiveStringViewTraits (and the underlying helper
case_insensitive_string_hash) to avoid allocations.
NoAllocationGuard is an RAII stack guard that prevents allocations
while it exists. This is done through a thread-local global flag which
causes malloc to crash on a VERIFY if it is false. The guard allows for
recursion.
The intended use case for this class is in real-time audio code. In such
code, allocations are really bad, and this is an easy way of dynamically
enforcing the no-allocations rule while giving the user good feedback if
it is violated. Before real-time audio code is executed, e.g. in LibDSP,
a NoAllocationGuard is instantiated. This is not done with this commit,
as currently some code in LibDSP may still incorrectly allocate in real-
time situations.
Other use cases for the Kernel have also been added, so this commit
builds on the previous to add the support both in Userland and in the
Kernel.
FixedArray now doesn't expose any infallible constructors anymore.
Rather, it exposes fallible methods. Therefore, it can be used for
OOM-safe code.
This commit also converts the rest of the system to use the new API.
However, as an example, VMObject can't take advantage of this yet,
as we would have to endow VMObject with a fallible static
construction method, which would require a very fundamental change
to VMObject's whole inheritance hierarchy.
