From 35612201f988fafd3495951a2885439ac62427e1 Mon Sep 17 00:00:00 2001
From: LoveSy <shana@zju.edu.cn>
Date: Tue, 27 Jun 2023 15:31:44 +0800
Subject: [PATCH] Lock-free JavaDebuggable guard

---
 lsplant/src/main/jni/lsplant.cc | 48 +++++++++++++++++++++++++++------
 1 file changed, 40 insertions(+), 8 deletions(-)

diff --git a/lsplant/src/main/jni/lsplant.cc b/lsplant/src/main/jni/lsplant.cc
index a77303b..81338b2 100644
--- a/lsplant/src/main/jni/lsplant.cc
+++ b/lsplant/src/main/jni/lsplant.cc
@@ -615,22 +615,54 @@ std::string GetProxyMethodShorty(JNIEnv *env, jobject proxy_method) {
 
 struct JavaDebuggableGuard {
     JavaDebuggableGuard() {
-        std::unique_lock lk(lock);
-        if (count.fetch_add(1, std::memory_order_acq_rel) == 0) {
-            Runtime::Current()->SetJavaDebuggable(
-                    Runtime::RuntimeDebugState::kJavaDebuggableAtInit);
+        while (true) {
+            size_t expected = 0;
+            if (count.compare_exchange_strong(expected, 1, std::memory_order_acq_rel,
+                                              std::memory_order_acquire)) {
+                Runtime::Current()->SetJavaDebuggable(
+                        Runtime::RuntimeDebugState::kJavaDebuggableAtInit);
+                count.fetch_add(1, std::memory_order_release);
+                count.notify_all();
+                break;
+            }
+            if (expected == 1) {
+                count.wait(expected, std::memory_order_acquire);
+                continue;
+            }
+            if (count.compare_exchange_strong(expected, expected + 1, std::memory_order_acq_rel,
+                                              std::memory_order_relaxed)) {
+                break;
+            }
         }
     }
 
     ~JavaDebuggableGuard() {
-        std::unique_lock lk(lock);
-        if (count.fetch_sub(1, std::memory_order_acq_rel) == 1) {
-            Runtime::Current()->SetJavaDebuggable(Runtime::RuntimeDebugState::kNonJavaDebuggable);
+        while (true) {
+            size_t expected = 2;
+            if (count.compare_exchange_strong(expected, 1, std::memory_order_acq_rel,
+                                              std::memory_order_acquire)) {
+                Runtime::Current()->SetJavaDebuggable(
+                        Runtime::RuntimeDebugState::kNonJavaDebuggable);
+                count.fetch_sub(1, std::memory_order_release);
+                count.notify_all();
+                break;
+            }
+            if (expected == 1) {
+                count.wait(expected, std::memory_order_acquire);
+                continue;
+            }
+            if (count.compare_exchange_strong(expected, expected - 1, std::memory_order_acq_rel,
+                                              std::memory_order_relaxed)) {
+                break;
+            }
         }
     }
 
+private:
     inline static std::atomic_size_t count{0};
-    inline static std::mutex lock;
+    static_assert(std::atomic_size_t::is_always_lock_free, "Unsupported architecture");
+    static_assert(std::is_same_v<std::atomic_size_t::value_type, size_t>,
+                  "Unsupported architecture");
 };
 
 }  // namespace