抽象:Mutex和std::atomic<>变量。 锁的acquire/release: mut_x.lock(); // “acquire” mut_x -> ld.acq mut_x … read/write x … mut_x.unlock(); // “release” mut_x -> st.rel mut_x std::atomic:读(read) = acquire,写(write) = release。 while( whose_turn != me ) { } /...
memory_order_acq_rel: 使用这种内存序的一个read-modify-write操作既是acquire操作也是release操作. 当前...
以保证读到的值是最新的, 此处和std::memory_order::memory_order_acquire是等价的....
Acquire/Release Acquire/release 对应std::memory_order_acquire和std::memory_order_acquire,它们的语义解释如下: Acquire:如果一个操作 X 带有 acquire 语义,那么在操作 X 后的所有load/store指令都不会被重排序到操作 X 之前,其他处理器会在看到操作X后序操作的影响之前看到操作 X 的影响,也就是必须先看到 X...
read-modify-write 操作即读 (load) 又写 (store), 它可以使用 memory_order_acquire, memory_order_release 和 memory_order_acq_rel:std::memory_order_consume:确保后续对依赖于当前原子操作结果的变量的读取是有序的。 使用: 多用于指针类型的原子6)内存模型 ...
只需要Read能直接访问这个Write Buffer,如下(注:这里的Load通常和Read等意,Store和Write等意): Release Consistency 在这种一致性下,所有的 memory operation ordering 都将不再维护,是最激进的一种内存一致模型,进入临界区叫做Acquire,离开临界区叫做Release。所有的memory operation ordering都将不再维护,处理器支持...
在RISC-V中safety net和原子指令有个交集,每个原子指令可以指定其aq/rl属性,即aquire/release属性,来强制其ordering。acquire允许前面的memory access推后,但不允许提前,release则相反,允许后面的memory access提前,但不允许推后。发布于 2020-11-28 21:42 ...
序列一致顺序(Sequential consistency):原子操作带上memory_order_seq_cst参数,这也是C++标准库的默认顺序,也是执行代价最大的,它是memory_order_acq_rel的加强版,如果是读取就是 acquire语义,如果是写入就是 release 语义,且全部读写操作顺序均一致。 下面代码中value = 100不允许被移动到readFlag.store(true, memo...
–Read from Memory –Modify –Write to Memory –Non-Atomic •Read/Write 64 Bits on 32 Bits Systems –Write:Non-Atomic –Read:Non-Atomic 2. Non-Atomic 的危害(在32位机上读写64位数如上图) •Half Write –mov dword ptr [c], 2 执行后,会短暂出现c的half write现象; ...
sorry for the strange questions but in my daily-job language (Java) there are no atomic read/write with relaxed order (until now) only read-acquire/write-release ones, hence the java memory model accustom the devs to use read-acquire/write-release for every thread communication... ...