Move MachPortServer from LibWebView into LibIPC as MachBootstrapListener
and move the Mach message structs from MachMessageTypes.h into LibIPC.
These types are IPC infrastructure, not UI or platform concerns.
Consolidating them in LibIPC keeps the Mach bootstrap handshake
self-contained in a single library and removes LibWebView's dependency
on LibThreading.
Now that LibIPC uses Mach ports for transport on macOS, IOSurface port
rights can be sent as regular IPC message attachments instead of through
a separate ad-hoc Mach message side-channel. Introduce
Web::SharedBackingStore that wraps either a MachPort (macOS) or
ShareableBitmap (other platforms) with IPC encode/decode support,
unifying backing store allocation into the existing
did_allocate_backing_stores IPC message.
On macOS, use Mach port messaging instead of Unix domain sockets for
all IPC transport. This makes the transport capable of carrying Mach
port rights as message attachments, which is a prerequisite for sending
IOSurface handles over the main IPC channel (currently sent via a
separate out-of-band path). It also avoids the need for the FD
acknowledgement protocol that TransportSocket requires, since Mach port
right transfers are atomic in the kernel.
Three connection establishment patterns:
- Spawned helper processes (WebContent, RequestServer, etc.) use the
existing MachPortServer: the child sends its task port with a reply
port, and the parent responds with a pre-created port pair.
- Socket-bootstrapped connections (WebDriver, BrowserProcess) exchange
Mach port names over the socket, then drop the socket.
- Pre-created pairs for IPC tests and in-message transport transfer.
Attachment on macOS now wraps a MachPort instead of a file descriptor,
converting between the two via fileport_makeport()/fileport_makefd().
The LibIPC socket transport tests are disabled on macOS since they are
socket-specific.
On macOS, Objective-C methods frequently return autoreleased objects
that accumulate until an autorelease pool is drained. Our event loop
(Core::EventLoop) and rendering thread both lacked autorelease pools,
causing unbounded accumulation of autoreleased objects.
The rendering thread was the worst offender: every Skia flush triggers
Metal resource allocation which sets labels on GPU textures via
-[IOGPUMetalResource setLabel:], creating autoreleased CFData objects.
With ~1M+ such objects at 112 bytes each, this leaked ~121MB. Metal
command buffer objects (_MTLCommandBufferEncoderInfo, etc.) also
accumulated, adding another ~128MB.
Add Core::ScopedAutoreleasePool, a RAII wrapper around the ObjC runtime
autorelease pool (no-op on non-macOS), and drain it:
- Every event loop pump (like NSRunLoop does)
- Every compositor loop iteration on the rendering thread
