Comments (4)
smuellerDD
commented on August 22, 2024
Am Dienstag, 20. Juni 2023, 14:08:44 CEST schrieb Wiktor Kwapisiewicz:
Hi Wiktor,
sorry for the delay.
Hello,
I'm working on improving [Rust bindings for
kcapi](https://github.com/puru1761/kcapi) and I'm pondering whether
`kcapi_handle`s in general are safe to use from multiple threads?
The library is reentrant, but the handles are not thread-safe. I.e. using the
handle by multiple threads requires a lock. This is due to the fact that the
handle contains state information which is updated with non-atomic operations.
Thus, when you have parallel threads using the same handle, you can get
inconsistent handles.
Yet, you have multiple handles (e.g. one per thread) then you do not need a
lock. I.e. the library and the AF_ALG iterface is fully thread-safe and you
can have multiple parallel requests (with multiple parallel handles).
I've been reading `kcapi.h` and there are quite a lot of mentions of "The
parallel execution can be performed in the same or different process
threads."
([source](https://github.com/smuellerDD/libkcapi/blob/master/lib/kcapi.h#L8
6)) and my local tests indicate that indeed multi-threaded access works
correctly (I've used hashing API).
Thank you for your insight and time! ๐
Ciao
Stephan
from libkcapi.
wiktor-k
commented on August 22, 2024
sorry for the delay.
No problem at all!
The library is reentrant, but the handles are not thread-safe. I.e. using the
handle by multiple threads requires a lock. This is due to the fact that the
handle contains state information which is updated with non-atomic operations.
Thus, when you have parallel threads using the same handle, you can get
inconsistent handles.
That clears a lot of my questions. One remains: can I move a handle from one thread to another? A hypothetical use case: I update the hash (kcapi_md_update) in one thread and then move that handle to another thread for hash finalization (kcapi_md_final). The handle would be used only by a single thread at a time but potentially by a different one throughout its lifetime. (I'm not sure if there are any thread local state in there).
Yet, you have multiple handles (e.g. one per thread) then you do not need a
lock. I.e. the library and the AF_ALG iterface is fully thread-safe and you
can have multiple parallel requests (with multiple parallel handles).
That's good to hear!
Thank you for help and this great library.
from libkcapi.
smuellerDD
commented on August 22, 2024
Am Donnerstag, 22. Juni 2023, 10:17:49 CEST schrieb Wiktor Kwapisiewicz:
Hi Wiktor,
> sorry for the delay.
No problem at all!
> The library is reentrant, but the handles are not thread-safe. I.e. using
> the
handle by multiple threads requires a lock. This is due to the fact that the
handle contains state information which is updated with non-atomic
operations. Thus, when you have parallel threads using the same handle, you
can get inconsistent handles.
That clears a lot of my questions. One remains: can I move a handle from one
thread to another?
Yes, always. Each API call may update the handle. But after the API call
completes, the handle is per definition always in a consistent state. In
addition, there is no state anywhere else that a handle relies on. Thus, a
handle is fully self-contained.
A hypothetical use case: I update the hash
(`kcapi_md_update`) in one thread and then move that handle to another
thread for hash finalization (`kcapi_md_final`). The handle would be used
only by a *single* thread at a time but potentially by a different one
throughout its lifetime. (I'm not sure if there are any thread local state
in there).
This is perfectly ok.
> Yet, you have multiple handles (e.g. one per thread) then you do not need
> a
lock. I.e. the library and the AF_ALG iterface is fully thread-safe and you
can have multiple parallel requests (with multiple parallel handles).
That's good to hear!
Thank you for help and this great library.
Thank you :-)
Ciao
Stephan
from libkcapi.
wiktor-k
commented on August 22, 2024
As everything concern has been resolved to completion I'm closing this issue.
Once again: your work is greatly appreciated and... have a nice day! ๐
from libkcapi.
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