Implement Lisp threading on Android

Much like the NS port, only the main thread receives input from
the user interface, which is fortunately not a major problem for
packages such as lsp-mode that create Lisp threads.

* configure.ac: Enable with_threads under Android.

* src/android.c (android_init_events): Set `main_thread_id' to
the ID of the main thread.
(setEmacsParams): Set new global variable `android_jvm' to the
JVM object, for the purpose of attaching Lisp threads to the
JVM.
(android_select): [THREADS_ENABLED]: If the caller isn't the
main thread, resort to pselect.  Don't check query before select
returns.
(android_check_query): Export.

* src/android.h (_ANDROID_H_): Define new macro and update
prototypes.

* src/process.c (android_select_wrapper): New function.
(wait_reading_process_output): If THREADS_ENABLED, call
thread_select through the Android select wrapper.

* src/thread.c (post_acquire_global_lock): Call
android_check_query; replace android_java_env with the incoming
Lisp thread's.
(run_thread): Attach and detach the thread created to the JVM.
(init_threads): Set the main thread's JNI environment object.

* src/thread.h (struct thread_state) <java_env>: New field.

1 files changed, 39 insertions, 0 deletions

diff --git a/src/thread.c b/src/thread.c
index 040ca39511e..2f5d7a08838 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -106,6 +106,12 @@ post_acquire_global_lock (struct thread_state *self)
 {
   struct thread_state *prev_thread = current_thread;
 
+  /* Switch the JNI interface pointer to the environment assigned to the
+     current thread.  */
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  android_java_env = self->java_env;
+#endif /* defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+
   /* Do this early on, so that code below could signal errors (e.g.,
      unbind_for_thread_switch might) correctly, because we are already
      running in the context of the thread pointed by SELF.  */
@@ -126,6 +132,12 @@ post_acquire_global_lock (struct thread_state *self)
       set_buffer_internal_2 (current_buffer);
     }
 
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  /* This step is performed in android_select when built without
+     threads.  */
+  android_check_query ();
+#endif /* defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+
    /* We could have been signaled while waiting to grab the global lock
       for the first time since this thread was created, in which case
       we didn't yet have the opportunity to set up the handlers.  Delay
@@ -756,6 +768,11 @@ run_thread (void *state)
 
   struct thread_state *self = state;
   struct thread_state **iter;
+#ifdef THREADS_ENABLED
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  jint rc;
+#endif /* #if defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+#endif /* THREADS_ENABLED */
 
 #ifdef HAVE_NS
   /* Allocate an autorelease pool in case this thread calls any
@@ -766,6 +783,16 @@ run_thread (void *state)
   void *pool = ns_alloc_autorelease_pool ();
 #endif
 
+#ifdef THREADS_ENABLED
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  rc
+    = (*android_jvm)->AttachCurrentThread (android_jvm, &self->java_env,
+                                           NULL);
+  if (rc != JNI_OK)
+    emacs_abort ();
+#endif /* defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+#endif /* THREADS_ENABLED */
+
   self->m_stack_bottom = self->stack_top = &stack_pos.c;
   self->thread_id = sys_thread_self ();
 
@@ -812,6 +839,14 @@ run_thread (void *state)
   ns_release_autorelease_pool (pool);
 #endif
 
+#ifdef THREADS_ENABLED
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  rc = (*android_jvm)->DetachCurrentThread (android_jvm);
+  if (rc != JNI_OK)
+    emacs_abort ();
+#endif /* defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+#endif /* THREADS_ENABLED */
+
   /* Unlink this thread from the list of all threads.  Note that we
      have to do this very late, after broadcasting our death.
      Otherwise the GC may decide to reap the thread_state object,
@@ -1131,6 +1166,10 @@ init_threads (void)
   sys_mutex_init (&global_lock);
   sys_mutex_lock (&global_lock);
   current_thread = &main_thread.s;
+#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
+  current_thread->java_env = android_java_env;
+#endif /* defined HAVE_ANDROID && !defined ANDROID_STUBIFY */
+
   main_thread.s.thread_id = sys_thread_self ();
   init_bc_thread (&main_thread.s.bc);
 }