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

[Alex Rousskov]

Amos Jeffries wrote:

> Please use std::atomic
> locks to ensure actually atomic operations on the file locks.

std::atomic<> is defined for integers and pointers. It is not defined
for "file locks", which are complex OS-maintained objects largely
invisible to Squid. C++11 std::atomic cannot magically make complex code
thread-safe (and still working as intended).


> 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.

Protecting File::File() try {...} with a mutex does not make File
objects thread-safe.


> 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.

By default, Squid code is not thread-safe and should not be thread-safe
because thread safety costs a lot (and Squid threads are isolated,
confined to a tiny subset of Squid code). Squid PID file management code
is not thread-safe. Squid parts those threads "reach" have to be
thread-safe, but they are not reaching the proposed code or the code it
replaces.

Please withdraw your request.


Thank you,

Alex.