Modified a non-volatile variable 100m times. Time used: 0.00 seconds Modified a volatile variable 100m times. Time used: 0.79 seconds 理解: 根据执行速度巨大差异, 或可推测, 前者(非 volatile 修饰)编译器或进行 register 类似优化, 而后者(volat
vd += vd * n*m;// reads and writes to a volatilefprintf(stdout,"Modified a volatile variable 100m times. Time used: %.2f seconds\n", (double)(clock() - t) / CLOCKS_PER_SEC); }return0; }/// reference: https://en.cppreference.com/w/cpp/language/cvinttest_volatile_3(){int...
1、openjdk8根路径/hotspot/src/share/vm/interpreter路径下的bytecodeInterpreter.cpp文件中,处理putstatic和putfield指令的代码: 1CASE(_putfield):2CASE(_putstatic):3{4//... 省略若干行5//...67//Now store the result 现在要开始存储结果了8//ConstantPoolCacheEntry* cache; -- cache是常量池缓存实例...
Now both pointers become a pointer to a volatile integer variable. In this situation, the compiler assumes that the value of the variable, which is pointed by a pointer can change unexpectedly at any time. So whenever we access *piData, the compiler is always aware of unexpected changes in ...
in which case the Java Memory Model ensures that all threads see a consistent value for the variable 从这段描述中我们可以知道 volatile 的语义了,它可以修饰 Java 对象中的字段,一旦某个字段被 volatile 修饰了,那么 Java 虚拟机会保证它在多个线程之间的可见性,也就是说,一个线程修改了这个字段,那么其他...
When an atomic load is performed on a shared variable, it reads the entire value as it appeared at a single moment in time. 1. 高级语言与汇编指令的映射 高级语言(如:C/C++),被编译为汇编语言,才能够被执行。因此,高级语言与汇编语言之间,存在着几种简单的映射关系。 •Simple Write –Write ...
(1) the content of a volatile variable is “unstable” (can change by means unknown to the compiler), (2) all writes to volatile data are “observable” so they must be executed religiously, and (3) all operations on volatile data are executed in the sequence in which they appear in ...
Theconstqualifier used on a declaration of a non-local non-volatilenon-template(since C++14)non-inline(since C++17)variable that is not declaredexterngives itinternal linkage. This is different from C where const file scope variables have external linkage. ...
1).并行设备的硬件寄存器（如：状态寄存器） 2).一个中断服务子程序中会访问到的非自动变量(Non-automaticvariables) 3).多线程应用中被几个任务共享的变量 回答不出这个问题的人是不会被雇佣的。我认为这是区分C程序员和嵌入式系统程序员的最基本的问题。嵌入式系统程序员经常同硬件、中断、RTOS等等打交道，所...
When used on a variable that also has the__restrictkeyword, volatile will take precedence. Example This program uses two features of volatile memory. It must honor all reads and writes from volatile memory; this allows it to be used for a mutex. ...