[squid-dev] [PATCH] Make PID file check/creation atomic

[Eduard Bagdasaryan]

Note that all PID-related methods are invoked before mainInitialize():
creating PID file ASAP was our goal here. Also, PID file operation
is a separate activity which has nothing common with DiskIO. In other
words, since DiskIO code knows nothing about PID file, it can't do any
harm with it.
I think your suggestion may be valuable but only after somebody
starts using File class in a threaded environment.


Eduard.

On 16.05.2017 15:21, Amos Jeffries wrote:
> On 16/05/17 01:42, Eduard Bagdasaryan wrote:
>> Could you clarify, what are these processes that 'operate as 
>> threads'? AFAIK,
>> Squid spawns its children by fork() and execlp(), and each new 
>> process is a
>> common process with its own address space. As for atomicity, the OS 
>> itself
>> guarantees that only one process can have an exclusive file lock at a
>> given time. Where do you suggest to use std::atomic then?
>>
>
> The main Squid binary is threaded via the DiskIO implementations (at 
> the least). These threads may be operational at any time after the 
> first StoreInit() call, and unfortunately do reach other parts of the 
> startup logic.
>
>
> An static std::atomic lock/flag around the File::File() try{...} 
> internals to make it threadsafe should resolve any potential issues 
> there, the fnctl locks should be able to cope with anything once the 
> lock() method returns.
>
>
> Amos
>
> _______________________________________________
> squid-dev mailing list
> squid-dev at lists.squid-cache.org
> http://lists.squid-cache.org/listinfo/squid-dev