Re: [RFC PATCH v1 2/2] chnet: Implement `get_thread()` and `put_thread()` function

[Ammar Nofan Faizi <ammar_nofan_faizi@yahoo.com>]

On 8/29/22 12:38 PM, Alviro Iskandar Setiawan wrote:
> On Mon, Aug 29, 2022 at 12:29 PM Ammar Nofan Faizi wrote:
>> On 8/29/22 12:24 PM, Alviro Iskandar Setiawan wrote:
>>> On Mon, Aug 29, 2022 at 12:17 PM Alviro Iskandar Setiawan wrote:
>>>> On Mon, Aug 29, 2022 at 11:54 AM Ammar Nofan Faizi wrote:
>>>>> On 8/29/22 11:41 AM, Alviro Iskandar Setiawan wrote:
>>>>>> On Mon, Aug 29, 2022 at 8:11 AM Ammar Faizi wrote:
>>>>>>> +static base::Thread *get_thread(void)
>>>>>>> +{
>>>>>>> +       const uint32_t max_ch_thpool = g_max_ch_thpool;
>>>>>>> +       const uint32_t nr_ref_split = 2048;
>>>>>>> +       struct ch_thpool **thp;
>>>>>>> +       struct ch_thpool *ret = nullptr;
>>>>>>> +       struct ch_thpool *tmp;
>>>>>>> +       uint32_t min_ref_idx;
>>>>>>> +       uint32_t min_ref;
>>>>>>> +       uint32_t i;
>>>>>>> +
>>>>>>> +       g_thpool_lock_.lock();
>>>>>>> +       thp = g_thpool;
>>>>>>> +       if (!thp) {
>>>>>>> +               g_thpool_lock_.unlock();
>>>>>>> +               return nullptr;
>>>>>>> +       }
>>>>>>
>>>>>> in what situation @thp can be nullptr?
>>>>>
>>>>> When the chnet_global_destroy() is called.
>>>
>>> btw, i missed a case on the chnet construction, you do
>>>
>>>      thread_(*get_thread()),
>>>
>>> if get_thread() returns a nullptr, the @thread_ will become a
>>> reference to a nullptr, it will definitely break, how do you handle
>>> this?
>>
>> I don't think we need to handle that. If @thp ever be a nullptr in a
>> get_thread() call, then it's a misuse of the API. We must never call
>> get_thread() after chnet_global_destroy() is called. It doesn't make
>> much sense to have this situation.
> 
> if this should never happen, then why do you do a null check there?
> your null check doesn't make much sense too! why are we returning
> nullptr if we exactly know that the caller will randomly fault if that
> happens, i can't accept your reasoning

OK.

Fine, let's omit that nullptr return. To assert that path, we perform a
CHECK() assertion, so it will just crash the whole program with a full
call traces if the contract is violated. This way also makes debugging
process easier. Are you happy with this change?

Incremental is:

diff --git a/chnet/chnet.cc b/chnet/chnet.cc
index 782e4fe..fc536d2 100644
--- a/chnet/chnet.cc
+++ b/chnet/chnet.cc
@@ -647,10 +647,7 @@ static base::Thread *get_thread(void)
  
  	g_thpool_lock_.lock();
  	thp = g_thpool;
-	if (!thp) {
-		g_thpool_lock_.unlock();
-		return nullptr;
-	}
+	CHECK(thp);
  
  	tmp = thp[0];
  	if (!tmp) {

-- 
Ammar Faizi