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design_pattern/singleton/cpulpuls11_singleton.cpp

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+//
+// Created by light on 20-2-7.
+//
+
+#include <iostream>
+
+using namespace std;
+
+#include <mutex>
+#include <atomic>
+
+//C++ 11版本之后的跨平台实现
+class singleton {
+private:
+    singleton() {}
+
+    static mutex lock_;
+    static atomic<singleton *> p;
+public:
+    singleton *instance();
+};
+
+mutex singleton::lock_;
+atomic<singleton *> singleton::p;
+
+/*
+* std::atomic_thread_fence(std::memory_order_acquire);
+* std::atomic_thread_fence(std::memory_order_release);
+* 这两句话可以保证他们之间的语句不会发生乱序执行。
+*/
+singleton *singleton::instance() {
+    singleton *tmp = p.load(memory_order_relaxed);
+    atomic_thread_fence(memory_order_acquire);
+    if (tmp == nullptr) {
+        lock_guard<mutex> guard(lock_);
+        tmp = p.load(memory_order_relaxed);
+        if (tmp == nullptr) {
+            tmp = new singleton();
+            atomic_thread_fence(memory_order_release);
+            p.store(tmp, memory_order_relaxed);
+        }
+    }
+    return p;
+}
+
+