資訊園

The Binder communicates between processes using a small custom kernel module. This is used instead of standard Linux IPC facilities so that we can efficiently model our IPC operations as "thread migration". That is, an IPC between processes looks as if the thread instigating the IPC has hopped over to the destination process to execute the code there, and then hopped back with the result.

The Binder IPC mechanism itself, however, is not actually implemented using thread migration. Instead, the Binder's user-space code maintains a pool of available threads in each process, which are used to process incoming IPCs and execute local events in that process. The kernel module emulates a thread migration model by propagating thread priorities across processes as IPCs are dispatched and ensuring that, if an IPC recurses back into an originating process, the IPC is handled by its originating thread.

In addition to IPC itself, the Binder's kernel module is also resposible for tracking object references across processes. This involves mapping from remote object references in one process to the real object in its host process, and making sure that objects are not destroyed as long as other processes hold references on them.