volatile C/C++ 中的volatile关键字和const对应,用来修饰变量,通常用于建立语言级别的 memory barrier。这是 BS 在 "The C++ Programming Language" 对 volatile 修饰词的说明: A volatile specifier is a hint to a compiler that an object may change its value in ways not specified by the language so tha...
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...
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...
我们翻开 11 HotSpot 的 src/hotspot/share/interpreter/bytecodeinterpreter.cpp 找到执行 getfield 和 getstatic 字节码执行的位置: ...CASE(_getfield):CASE(_getstatic):{...if(cache->is_volatile()){if(support_IRIW_for_not_multiple_copy_atomic_cpu){OrderAccess::fence();}...}...} 可以 看到,...
volatile关键字可以用来修饰变量，通常放在变量类型的前面，语法如下：cpp volatileintmyVariable;这样就声明了一个volatile修饰的int类型变量myVariable。在嵌入式系统编程中，常常需要和硬件寄存器进行交互。硬件寄存器的值可能会因为外部事件（如硬件中断、传感器数据更新等）而发生改变，这些改变无法被程序代码直接控制。此时...
Modified a volatile variable 100m times. Time used: 0.79 seconds 理解: 根据执行速度巨大差异, 或...
最后附上《Java Concurrency in Practice》3.1.4节中对Java语言的volatile关键字的使用建议(不要被英语吓到,这些内容确实对你有用,而且还能顺便帮练练英语,哈哈): So from a memory visibility perspective, writing a volatile variable is like exiting a synchronized block and reading a volatile variable is lik...
(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 ...
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 ...
When volatile is used on a variable that also has the __restrict keyword, volatile takes precedence. If a struct member is marked as volatile, then volatile is propagated to the whole structure. If a structure does not have a length that can be copied on the current architecture by using ...