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doc: Update Android IPC section

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Jarvis Huang 2021-12-08 15:12:10 +08:00 committed by Ryan Pavlik
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@ -5,7 +5,7 @@ Copyright 2021, Collabora, Ltd. and the Monado contributors
SPDX-License-Identifier: BSL-1.0 SPDX-License-Identifier: BSL-1.0
--> -->
- Last updated: 24-February-2021 - Last updated: 8-December-2021
When the service starts, an `xrt_instance` is created and selected, a native When the service starts, an `xrt_instance` is created and selected, a native
system compositor is initialized, a shared memory segment for device data is system compositor is initialized, a shared memory segment for device data is
@ -80,15 +80,15 @@ APK, even though they get loaded in different processes.
The first main purpose of this service is for automatic startup and the The first main purpose of this service is for automatic startup and the
**locating** function: helping establish communication between the client and **locating** function: helping establish communication between the client and
the service. The Android framework takes care of launching the service process the service. The Android framework takes care of launching the service process
when the client requests to start and bind our service by name and package. The when the client requests to bind our service by name and package. The framework
framework also provides us with method calls when we're started/bound. In this also provides us with method calls when we're bound. In this way, the "entry point"
way, the "entry point" of the Monado service on Android is the of the Monado service on Android is the
`org.freedesktop.monado.ipc.MonadoService` class, which exposes the `org.freedesktop.monado.ipc.MonadoService` class, which exposes the
implementation of our AIDL interface, `org.freedesktop.monado.ipc.MonadoImpl`. implementation of our AIDL interface, `org.freedesktop.monado.ipc.MonadoImpl`.
From there, the native-code mainloop starts when this service is started. By From there, the native-code mainloop starts when this service received a valid
default, the JVM code will signal the mainloop to shut down a short time after `Surface`. By default, the JVM code will signal the mainloop to shut down a short
the last client disconnects, to work best within the platform. time after the last client disconnects, to work best within the platform.
At startup, just as on Linux, the shared memory segment is created. The At startup, just as on Linux, the shared memory segment is created. The
[ashmem][] API is used to create/destroy an anonymous **shared memory** segment [ashmem][] API is used to create/destroy an anonymous **shared memory** segment
@ -107,9 +107,18 @@ connecting/accepting the named socket as used in standard Linux.
The AIDL interface is also used for transporting some platform objects. At this The AIDL interface is also used for transporting some platform objects. At this
time, the only one transported in this way is the [Surface][] injected into the time, the only one transported in this way is the [Surface][] injected into the
client activity which is used for displaying rendered output. client activity which is used for displaying rendered output. Surface only comes
from client when [Display over other apps][] is disabled.
The owner of surface will impact the service shutdown behavior. When the
surface comes from the injected window, it becomes invalid when client activity
destroys. Therefore the runtime service must be shutdown when client exits,
because all the graphic resources are associated with that surface. On the other
hand, when the owner of surface is the runtime service, it's capable to support
multiple clients and client transition without shutdown.
[Surface]: https://developer.android.com/reference/android/view/Surface [Surface]: https://developer.android.com/reference/android/view/Surface
[Display over other apps]: https://developer.android.com/reference/android/Manifest.permission#SYSTEM_ALERT_WINDOW
### Synchronization ### Synchronization