Re: boost::asio::deadline_timer and boost::asio::io_service

From: Gavin Lambert (boost_at_[hidden])
Date: 2019-09-02 02:52:22

On 2/09/2019 13:06, JH wrote:
> Does io_service create threads for running timers? My application is
> running a single thread, but if io_service creates multiple threads
> for running timer, I must use the mutex or atomic lock.

Don't top-post.

As is documented, while Asio may or may not create internal threads for 
various purposes, it does guarantee that the I/O callback functions 
(including timer callbacks) are only ever called on a thread which is 
currently executing run() or equivalent on the same service/context.

If there is only one such thread (an "implicit strand"), then you don't 
need locks to protect things that are only accessed from an I/O 
callback, even if there is more than one such callback (provided that 
all callbacks were registered on the same service/context).

You may still need locks to protect things that are accessed from both 
callbacks and initiating functions (or elsewhere), unless you ensure 
that initiating functions delegate their concurrent work to the I/O 
thread via dispatch()/post().