blob: 4e46ba1edc34f77fb6a8074e838399fd77f3e1ea [file] [log] [blame]
.. title:: clang-tidy - concurrency-mt-unsafe
Checks for some thread-unsafe functions against a black list of
known-to-be-unsafe functions. Usually they access static variables without
synchronization (e.g. gmtime(3)) or utilize signals in a racy way.
The set of functions to check is specified with the `FunctionSet` option.
Note that using some thread-unsafe functions may be still valid in
concurrent programming if only a single thread is used (e.g. setenv(3)),
however, some functions may track a state in global variables which
would be clobbered by subsequent (non-parallel, but concurrent) calls to
a related function. E.g. the following code suffers from unprotected
accesses to a global state:
.. code-block:: c++
// getnetent(3) maintains global state with DB connection, etc.
// If a concurrent green thread calls getnetent(3), the global state is corrupted.
netent = getnetent();
netent = getnetent();
.. code-block:: c++
tm = gmtime(timep); // uses a global buffer
sleep(1); // implementation may use SIGALRM
.. option:: FunctionSet
Specifies which functions in libc should be considered thread-safe,
possible values are `posix`, `glibc`, or `any`.
`posix` means POSIX defined thread-unsafe functions. POSIX.1-2001
in "2.9.1 Thread-Safety" defines that all functions specified in the
standard are thread-safe except a predefined list of thread-unsafe
Glibc defines some of them as thread-safe (e.g. dirname(3)), but adds
non-POSIX thread-unsafe ones (e.g. getopt_long(3)). Glibc's list is
compiled from GNU web documentation with a search for MT-Safe tag:
If you want to identify thread-unsafe API for at least one libc or
unsure which libc will be used, use `any` (default).