Wait GC to complete before each hook

Bridge/src/main/java/com/elderdrivers/riru/xposed/Main.java

@@ -129,4 +129,6 @@ public class Main implements KeepAll {
     public static native long suspendAllThreads();
 
     public static native void resumeAllThreads(long obj);
+
+    public static native int waitForGcToComplete(long thread);
 }

Bridge/src/main/java/com/elderdrivers/riru/xposed/core/HookMain.java

@@ -1,5 +1,6 @@
 package com.elderdrivers.riru.xposed.core;
 
+import com.elderdrivers.riru.xposed.Main;
 import com.elderdrivers.riru.xposed.entry.hooker.OnePlusWorkAroundHooker;
 import com.elderdrivers.riru.xposed.util.Utils;
 
@@ -11,6 +12,8 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.Set;
 
+import de.robv.android.xposed.XposedHelpers;
+
 import static com.elderdrivers.riru.xposed.Main.backupAndHookNative;
 import static com.elderdrivers.riru.xposed.Main.findMethodNative;
 
@@ -111,7 +114,14 @@ public class HookMain {
         if (backup != null) {
             HookMethodResolver.resolveMethod(hook, backup);
         }
-        Runtime.getRuntime().gc();
+        // make sure GC completed before hook
+        Thread currentThread = Thread.currentThread();
+        int lastGcType = Main.waitForGcToComplete(
+                XposedHelpers.getLongField(currentThread, "nativePeer"));
+        if (lastGcType < 0) {
+            Utils.logW("waitForGcToComplete failed, using fallback");
+            Runtime.getRuntime().gc();
+        }
         if (!backupAndHookNative(target, hook, backup)) {
             throw new RuntimeException("Failed to hook " + target + " with " + hook);
         }

Core/jni/main/java_hook/java_hook.cpp

@@ -52,6 +52,12 @@ void resumeAllThreads(JNIEnv *, jclass, jlong obj) {
     resumeAll(reinterpret_cast<ScopedSuspendAll *>(obj));
 }
 
+int waitForGcToComplete(JNIEnv *, jclass, jlong thread) {
+    // if waitGc succeeded, it should return one of enum collector::GcType
+    int gcType = waitGc(0, reinterpret_cast<void *>(thread));
+    return gcType;
+}
+
 static JNINativeMethod hookMethods[] = {
         {
                 "init",
@@ -99,6 +105,9 @@ static JNINativeMethod hookMethods[] = {
         },
         {
                 "resumeAllThreads", "(J)V", (void *) resumeAllThreads
+        },
+        {
+                "waitForGcToComplete", "(J)I", (void *) waitForGcToComplete
         }
 };
 
@@ -137,7 +146,7 @@ void loadDexAndInit(JNIEnv *env, const char *dexPath) {
     jclass entry_class = findClassFromLoader(env, myClassLoader, ENTRY_CLASS_NAME);
     if (NULL != entry_class) {
         LOGD("HookEntry Class %p", entry_class);
-        env->RegisterNatives(entry_class, hookMethods, 13);
+        env->RegisterNatives(entry_class, hookMethods, 14);
         isInited = true;
         LOGD("RegisterNatives succeed for HookEntry.");
     } else {

Core/jni/main/native_hook/native_hook.cpp

@@ -28,6 +28,8 @@ static void *(*instrCstBackup)(void *instru) = nullptr;
 
 void (*deoptMethod)(void *, void *) = nullptr;
 
+static void (*heapPreForkBackup)(void *) = nullptr;
+
 bool my_runtimeInit(void *runtime, void *mapAddr) {
     if (!runtimeInitBackup) {
         LOGE("runtimeInitBackup is null");
@@ -212,17 +214,49 @@ void hookRuntime(int api_level, void *artHandle, void (*hookFun)(void *, void *,
     }
 }
 
-void (*suspendAll)(ScopedSuspendAll*, const char*, bool) = nullptr;
-void (*resumeAll)(ScopedSuspendAll*) = nullptr;
+void (*suspendAll)(ScopedSuspendAll *, const char *, bool) = nullptr;
+
+void (*resumeAll)(ScopedSuspendAll *) = nullptr;
+
+int (*waitGcInternal)(void *, int, void *) = nullptr;
+
+void *heap_ = nullptr;
+
+int waitGc(int gcCause, void *thread) {
+    if (!heap_) {
+        LOGE("heap_ is null");
+        return -1;
+    }
+    return (*waitGcInternal)(heap_, gcCause, thread);
+}
+
+static void myHeapPreFork(void *heap) {
+    heap_ = heap;
+    (*heapPreForkBackup)(heap);
+}
 
 void getSuspendSyms(int api_level, void *artHandle, void (*hookFun)(void *, void *, void **)) {
-    if (api_level < ANDROID_N) {
-        return;
+    if (api_level >= ANDROID_LOLLIPOP) {
+        waitGcInternal = reinterpret_cast<int (*)(void *, int, void *)>(dlsym(artHandle,
+                                                                              "_ZN3art2gc4Heap19WaitForGcToCompleteENS0_7GcCauseEPNS_6ThreadE"));
+        void *heapPreFork = dlsym(artHandle, "_ZN3art2gc4Heap13PreZygoteForkEv");
+        if (!heapPreFork) {
+            LOGE("can't find heapPreFork: %s", dlerror());
+        } else {
+            // a chance to get pointer of the heap
+            (*hookFun)(heapPreFork, reinterpret_cast<void *>(myHeapPreFork),
+                       reinterpret_cast<void **>(&heapPreForkBackup));
+            LOGI("heapPreFork hooked.");
+        }
+    }
+
+    if (api_level >= ANDROID_N) {
+        suspendAll = reinterpret_cast<void (*)(ScopedSuspendAll *, const char *, bool)>(dlsym(
+                artHandle,
+                "_ZN3art16ScopedSuspendAllC2EPKcb"));
+        resumeAll = reinterpret_cast<void (*)(ScopedSuspendAll *)>(dlsym(artHandle,
+                                                                         "_ZN3art16ScopedSuspendAllD2Ev"));
     }
-    suspendAll = reinterpret_cast<void (*)(ScopedSuspendAll*,const char*, bool)>(dlsym(artHandle,
-                                                        "_ZN3art16ScopedSuspendAllC2EPKcb"));
-    resumeAll = reinterpret_cast<void (*)(ScopedSuspendAll*)>(dlsym(artHandle,
-                                                            "_ZN3art16ScopedSuspendAllD2Ev"));
 }
 
 void install_inline_hooks() {

Core/jni/main/native_hook/native_hook.h

@@ -26,6 +26,8 @@ extern void (*suspendAll)(ScopedSuspendAll *, const char *, bool);
 
 extern void (*resumeAll)(ScopedSuspendAll *);
 
+extern int waitGc(int, void *);
+
 void install_inline_hooks();
 
 void deoptimize_method(JNIEnv *env, jclass clazz, jobject method);