I was trying to find the answer for some time but I failed.
Lets assume that we have a shared_ptr
created from one thread. Then we pass this shared_ptr
to another 2 threads (using some queue for example). So from this moment there are 2 copies of the original shared_ptr
, pointing to the same raw pointer.
Both owner threads will take their copies of this shared_ptr
from the queue. Then they will pass it to another thread or will destroy it.
Question is - is it safe? Will the raw pointer destroyed correctly (there will be no race to reference counter?)
The boost docs state:
Different shared_ptr instances can be "written to" (accessed using mutable operations such as operator= or reset) simultaneosly by multiple threads (even when these instances are copies, and share the same reference count underneath.)
(emphasis mine)
So the crux here is whether you copy the boost::shared_ptr
s between threads or not. If you create copies (the "safe" way to use shared_ptr
s) you don't have any worries about thread-safety. If however you pass the shared_ptr
by reference or pointer, and hence are using the actual same shared_ptr
in different threads, you would have to worry about thread-safety, as described in the docs.