libbinder: simpler scope_guard implementation

libbinder_on_trusty_mock size: 289,374 -> 286,533 bytes

Bug: 338458975
Test: TH
Change-Id: I9fc817ba09c8697fb8b5f566cec28f15b6e7ea5d

1 files changed, 28 insertions, 7 deletions

diff --git a/libs/binder/include/binder/Functional.h b/libs/binder/include/binder/Functional.h
index 08e3b214da..bb0e5f4115 100644
--- a/libs/binder/include/binder/Functional.h
+++ b/libs/binder/include/binder/Functional.h
@@ -17,11 +17,38 @@
 #pragma once
 
 #include <functional>
-#include <memory>
+#include <optional>
 
 namespace android::binder::impl {
 
 template <typename F>
+class scope_guard;
+
+template <typename F>
+scope_guard<F> make_scope_guard(F f);
+
+template <typename F>
+class scope_guard {
+public:
+    inline ~scope_guard() {
+        if (f_.has_value()) std::move(f_.value())();
+    }
+    inline void release() { f_.reset(); }
+
+private:
+    friend scope_guard<F> android::binder::impl::make_scope_guard(F);
+
+    inline scope_guard(F&& f) : f_(std::move(f)) {}
+
+    std::optional<F> f_;
+};
+
+template <typename F>
+inline scope_guard<F> make_scope_guard(F f) {
+    return scope_guard<F>(std::move(f));
+}
+
+template <typename F>
 constexpr void assert_small_callable() {
     // While this buffer (std::function::__func::__buf_) is an implementation detail generally not
     // accessible to users, it's a good bet to assume its size to be around 3 pointers.
@@ -32,12 +59,6 @@ constexpr void assert_small_callable() {
                   "Try using std::ref, but make sure lambda lives long enough to be called.");
 }
 
-template <typename F>
-std::unique_ptr<void, std::function<void(void*)>> make_scope_guard(F&& f) {
-    assert_small_callable<decltype(std::bind(f))>();
-    return {reinterpret_cast<void*>(true), std::bind(f)};
-}
-
 template <typename T>
 class SmallFunction : public std::function<T> {
 public: