From c947f2cf0ddcd38b6775fa48dade8158ded6210f Mon Sep 17 00:00:00 2001
From: Fabien Sanglard <sanglardf@google.com>
Date: Wed, 16 Nov 2022 17:20:22 -0800
Subject: Remove 1.3s "Waiting for Debugger" delay

Remove arbitrary loop when a debugged app starts. Instead for waiting
for 1.3 seconds, we instruct oj-jdwplib to suspendfor all the threads
and sent VM_START. We continue as soon as the debugger sends ResumeAll.

Design doc: go/waitingfordebugger

Test: Manually tested against Android Studio and jdb
Bug: 261096302

Change-Id: I76c02d6acd0d7fb5babed0018432db74ae29487e
---
 core/java/android/os/Debug.java | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/core/java/android/os/Debug.java b/core/java/android/os/Debug.java
index 399f11b0f2a7..c731a808263a 100644
--- a/core/java/android/os/Debug.java
+++ b/core/java/android/os/Debug.java
@@ -981,6 +981,43 @@ public final class Debug
     }
 
 
+    /**
+     * Wait until a debugger attaches. As soon as a debugger attaches,
+     * suspend all Java threads and send VM_START (a.k.a VM_INIT)
+     * packet.
+     *
+     * @hide
+     */
+    public static void suspendAllAndSendVmStart() {
+        if (!VMDebug.isDebuggingEnabled()) {
+            return;
+        }
+
+        // if DDMS is listening, inform them of our plight
+        System.out.println("Sending WAIT chunk");
+        byte[] data = new byte[] { 0 };     // 0 == "waiting for debugger"
+        Chunk waitChunk = new Chunk(ChunkHandler.type("WAIT"), data, 0, 1);
+        DdmServer.sendChunk(waitChunk);
+
+        // We must wait until a debugger is connected (debug socket is
+        // open and at least one non-DDM JDWP packedt has been received.
+        // This guarantees that oj-libjdwp has been attached and that
+        // ART's default implementation of suspendAllAndSendVmStart has
+        // been replaced with an implementation that will suspendAll and
+        // send VM_START.
+        System.out.println("Waiting for debugger first packet");
+        while (!isDebuggerConnected()) {
+            try {
+                Thread.sleep(100);
+            } catch (InterruptedException ie) {
+            }
+        }
+
+        System.out.println("Debug.suspendAllAndSentVmStart");
+        VMDebug.suspendAllAndSendVmStart();
+        System.out.println("Debug.suspendAllAndSendVmStart, resumed");
+    }
+
     /**
      * Wait until a debugger attaches.  As soon as the debugger attaches,
      * this returns, so you will need to place a breakpoint after the
-- 
cgit v1.2.3-59-g8ed1b