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Posted to dev@brpc.apache.org by GitBox <gi...@apache.org> on 2020/06/29 16:30:13 UTC
[GitHub] [incubator-brpc] triump2020 opened a new issue #1150: resource_pool_inl.h 中 add_block 函数 关于Lock-Free 的问题??
triump2020 opened a new issue #1150:
URL: https://github.com/apache/incubator-brpc/issues/1150
Hi Contributors and Jamesge !
Brpc 在性能上确实优于很多目前rpc 框架， 但是在看源码过程中，发现resource_pool_inl.h 中 add_block 函数好像有个问题, 当然也有可能是我的误解，望解答，谢谢！ 下面是add_block 函数中的 一个do-while 循环，问题出在do-while 的最后返回new_block 的地方，这个new_block 在返回之前，没有加Acquire 语义。
do {
//这里的_ngroup 不一定能拿到最新值.
ngroup = _ngroup.load(butil::memory_order_acquire);
if (ngroup >= 1) {
BlockGroup* const g =
_block_groups[ngroup - 1].load(butil::memory_order_consume);
const size_t block_index =
g->nblock.fetch_add(1, butil::memory_order_relaxed);
// 如果上面的_ngroup 取到的是一个旧值，则下面的if 条件不会成立
// 然后进入add_block_group, 而add_block_group 里有加锁操作
// 可以拿到最新的_ngroup 值， 程序是安全的.
if (block_index < RP_GROUP_NBLOCK) {
// ****问题：****
// 这里strore用了release 语义，
// 但是返回new_block 之前，没有加上对应的Acquire语义???
g->blocks[block_index].store(
new_block, butil::memory_order_release);
*index = (ngroup - 1) * RP_GROUP_NBLOCK + block_index;
return new_block;
}
g->nblock.fetch_sub(1, butil::memory_order_relaxed);
}
} while (add_block_group(ngroup));
**Describe the bug (描述bug)**
**To Reproduce (复现方法)**
**Expected behavior (期望行为)**
**Versions (各种版本)**
OS:
Compiler:
brpc:
protobuf:
**Additional context/screenshots (更多上下文/截图)**
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[GitHub] [incubator-brpc] triump2020 closed issue #1150: resource_pool_inl.h 中 add_block 函数 关于Lock-Free 的问题??
Posted by GitBox <gi...@apache.org>.
triump2020 closed issue #1150:
URL: https://github.com/apache/incubator-brpc/issues/1150
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[GitHub] [incubator-brpc] triump2020 commented on issue #1150: resource_pool_inl.h 中 add_block 函数 关于Lock-Free 的问题??
Posted by GitBox <gi...@apache.org>.
triump2020 commented on issue #1150:
URL: https://github.com/apache/incubator-brpc/issues/1150#issuecomment-652131514
同一个线程里，对同一个原子变量的读写不会乱序
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