Serialize io_service::post() execution with io_service::run() called only in a single thread

Question

如果我只在一个线程中运行io_service::run() ， io_service::post()调用是按照我请求它们执行的相同顺序执行的，或者它们可以按任意顺序执行，我仍然需要使用用于强制序列化执行的strand ？

Answer 1

The question has been treated before, eg

• Does boost::asio::io_service preserve the order of handlers? ?
• Documentation: Oreder Of Handler Invocations

It clearly spells out

if any of the following conditions are true:

• s.post(a) happens-before s.post(b)
• ...

then asio_handler_invoke(a1, &a1) happens-before asio_handler_invoke(b1, &b1) .

Note that a single IO thread creates the implicit strand (docs)

---

Note In relation to the other answer: of course this doesn't hold when the handler invocations are done implicitly on completion of an asynchronous operation.

Note that in the following case:

 async_op_1(..., s.wrap(a)); async_op_2(..., s.wrap(b)); 

the completion of the first async operation will perform s.dispatch(a) , and the second will perform s.dispatch(b) , but the order in which those are performed is unspecified. That is, you cannot state whether one happens-before the other. Therefore none of the above conditions are met and no ordering guarantee is made.