[dpdk-users] Membership library thread safety

Wang, Yipeng1 yipeng1.wang at intel.com
Sat Jun 2 00:16:46 CEST 2018


You are right that It is similar to other rte data structure that you can initialize it in a master thread and do lookup in other threads.

w.r.t. concurrency,  the original plan is to have the fastest data structure used mostly per-thread basis so any locking/atomicity guarantee is too costly.

So for non-cache mode HT based setsum, since deletion is supported and false-negative is not supposed to happen, I would say it only supports single writer/delete thread.  For read-write concurrency, due to the "cuckoo hash" algorithm, there might be a short window (very unlikely) that a key lookup could return an intermediate result while another thread writing to the table. Depending on how your application could tolerate such case, you may or may not want to use it for read-write concurrency. One option is to turn off the cuckoo algorithm if you would like to play with the code a little bit.

Vector BF also only supports single writer if you don't want false negative, but read-write concurrency should be fine

For cache mode HT based setsum, things are less restrictive. Since it is supposed to be used as a cache and both false-negative and false-positive are allowed, it would be fine for multiple writer writing concurrently. 

Note that you can always use multiple readers concurrently.

If possible, may I ask for the use case you have? The purpose is to make the library more usable. Feel free to propose new patches as well. If concurrency is definitely a requirement, we could collaborate on new concurrency APIs. We will improve the documentation as well to state things more clearly.


>-----Original Message-----
>From: longtb5 at viettel.com.vn [mailto:longtb5 at viettel.com.vn]
>Sent: Friday, June 1, 2018 12:10 AM
>To: users at dpdk.org
>Cc: Wang, Yipeng1 <yipeng1.wang at intel.com>; Gobriel, Sameh <sameh.gobriel at intel.com>
>Subject: Membership library thread safety
>I'm using rte_member in my application. I have two questions.
>1. Could a rte_member_setsum be initialized on one thread and used on
>another thread?
>2. Are the operations (lookup, add, reset,.) atomic, or do I need to use
>some kind of locking (e.g. rte_spinlock)?
>I couldn't find anything in the doc. My guess is that you can init and use a
>setsum on different threads just fine, but sharing a setsum among different
>threads does require locking.
>Thanks and best regards,

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