Previously, the bootstrap handshake used a two-state machine
(WaitingForPorts / WaitingForReplyPort) to handle a race: the parent
registering transport ports and the child sending a bootstrap request
could arrive in either order, so whichever came first stored its half
and the second completed the handshake.
Eliminate the race by holding a mutex across spawn() and
register_child_transport(). Since the child cannot send a bootstrap
request before it exists, and the lock isn't released until its
transport is registered, handle_bootstrap_request() is guaranteed to
find the entry. This reduces the pending map to a simple pid-to-ports
lookup and collapses the two-variant state into two straightforward
branches: known child, or on-demand (non-child) caller like WebDriver.
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.
Registering multiple Mach port names with the bootstrap server at
runtime is not how macOS expects it to be used — the bootstrap server
is meant for static services, and the only reason we used it originally
was so child processes could reach back to the UI process.
Remove bootstrap_transport_over_socket(), which had both sides register
dynamic names with the bootstrap server and exchange them over a socket.
Instead, WebDriver and BrowserProcess connections now go through
MachPortServer instances directly. When a non-child process contacts a
MachPortServer, the server creates a port pair on demand (detected via
sysctl ppid check) and returns the local half immediately. This keeps
bootstrap server usage limited to the one original case: child processes
looking up their parent's MachPortServer.
WebDriver Session now runs its own MachPortServer per session.
--webdriver-content-path becomes --webdriver-mach-server-name on macOS.
Spare WebContent launches are skipped when a WebDriver session is active
to avoid bootstrap races.
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.
