From 5324723c2bcab7062f393a5057e51733a1715788 Mon Sep 17 00:00:00 2001
From: Po Lu <luangruo@yahoo.com>
Date: Fri, 10 Nov 2023 14:57:24 +0800
Subject: [PATCH] Clear image caches in reaction to system VM warnings

* java/org/gnu/emacs/EmacsNative.java (onLowMemory):

* java/org/gnu/emacs/EmacsService.java (onLowMemory): New
function.

* src/android.c (android_on_low_memory, onLowMemory): New
functions called when a VM caution is registered.  Clear
the image cache and run garbage collection.
---
 java/org/gnu/emacs/EmacsNative.java  |  3 +++
 java/org/gnu/emacs/EmacsService.java | 12 ++++++++++++
 src/android.c                        | 20 ++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/java/org/gnu/emacs/EmacsNative.java b/java/org/gnu/emacs/EmacsNative.java
index 946a38f7f84..78176dd0e47 100644
--- a/java/org/gnu/emacs/EmacsNative.java
+++ b/java/org/gnu/emacs/EmacsNative.java
@@ -96,6 +96,9 @@ public final class EmacsNative
      thread, then return.  */
   public static native void shutDownEmacs ();
 
+  /* Garbage collect and clear each frame's image cache.  */
+  public static native void onLowMemory ();
+
   /* Abort and generate a native core dump.  */
   public static native void emacsAbort ();
 
diff --git a/java/org/gnu/emacs/EmacsService.java b/java/org/gnu/emacs/EmacsService.java
index ab6d57b9c4f..1aac1a6c4dd 100644
--- a/java/org/gnu/emacs/EmacsService.java
+++ b/java/org/gnu/emacs/EmacsService.java
@@ -321,6 +321,10 @@ public final class EmacsService extends Service
       }
   }
 
+  /* The native functions the subsequent two functions call do nothing
+     in the infrequent case the Emacs thread is awaiting a response
+     for the main thread.  Caveat emptor! */
+
   @Override
   public void
   onDestroy ()
@@ -333,6 +337,14 @@ public final class EmacsService extends Service
     super.onDestroy ();
   }
 
+  @Override
+  public void
+  onLowMemory ()
+  {
+    EmacsNative.onLowMemory ();
+    super.onLowMemory ();
+  }
+
 
 
   /* Functions from here on must only be called from the Emacs
diff --git a/src/android.c b/src/android.c
index f5af742b422..7a670cb507f 100644
--- a/src/android.c
+++ b/src/android.c
@@ -1957,6 +1957,26 @@ NATIVE_NAME (shutDownEmacs) (JNIEnv *env, jobject object)
   android_run_in_emacs_thread (android_shut_down_emacs, NULL);
 }
 
+/* Carry out garbage collection and clear all image caches on the
+   Android terminal.  Called when the system has depleted most of its
+   memory and desires that background processes release unused
+   core.  */
+
+static void
+android_on_low_memory (void *closure)
+{
+  Fclear_image_cache (Qt, Qt);
+  garbage_collect ();
+}
+
+JNIEXPORT void JNICALL
+NATIVE_NAME (onLowMemory) (JNIEnv *env, jobject object)
+{
+  JNI_STACK_ALIGNMENT_PROLOGUE;
+
+  android_run_in_emacs_thread (android_on_low_memory, NULL);
+}
+
 JNIEXPORT jlong JNICALL
 NATIVE_NAME (sendConfigureNotify) (JNIEnv *env, jobject object,
 				   jshort window, jlong time,
-- 
2.39.2