1*6e566bc5SRichard.. title:: clang-tidy - concurrency-mt-unsafe 2*6e566bc5SRichard 3*6e566bc5SRichardconcurrency-mt-unsafe 4*6e566bc5SRichard===================== 5*6e566bc5SRichard 6*6e566bc5SRichardChecks for some thread-unsafe functions against a black list of 7*6e566bc5SRichardknown-to-be-unsafe functions. Usually they access static variables without 8*6e566bc5SRichardsynchronization (e.g. gmtime(3)) or utilize signals in a racy way. 9*6e566bc5SRichardThe set of functions to check is specified with the `FunctionSet` option. 10*6e566bc5SRichard 11*6e566bc5SRichardNote that using some thread-unsafe functions may be still valid in 12*6e566bc5SRichardconcurrent programming if only a single thread is used (e.g. setenv(3)), 13*6e566bc5SRichardhowever, some functions may track a state in global variables which 14*6e566bc5SRichardwould be clobbered by subsequent (non-parallel, but concurrent) calls to 15*6e566bc5SRicharda related function. E.g. the following code suffers from unprotected 16*6e566bc5SRichardaccesses to a global state: 17*6e566bc5SRichard 18*6e566bc5SRichard.. code-block:: c++ 19*6e566bc5SRichard 20*6e566bc5SRichard // getnetent(3) maintains global state with DB connection, etc. 21*6e566bc5SRichard // If a concurrent green thread calls getnetent(3), the global state is corrupted. 22*6e566bc5SRichard netent = getnetent(); 23*6e566bc5SRichard yield(); 24*6e566bc5SRichard netent = getnetent(); 25*6e566bc5SRichard 26*6e566bc5SRichard 27*6e566bc5SRichardExamples: 28*6e566bc5SRichard 29*6e566bc5SRichard.. code-block:: c++ 30*6e566bc5SRichard 31*6e566bc5SRichard tm = gmtime(timep); // uses a global buffer 32*6e566bc5SRichard 33*6e566bc5SRichard sleep(1); // implementation may use SIGALRM 34*6e566bc5SRichard 35*6e566bc5SRichard.. option:: FunctionSet 36*6e566bc5SRichard 37*6e566bc5SRichard Specifies which functions in libc should be considered thread-safe, 38*6e566bc5SRichard possible values are `posix`, `glibc`, or `any`. 39*6e566bc5SRichard 40*6e566bc5SRichard `posix` means POSIX defined thread-unsafe functions. POSIX.1-2001 41*6e566bc5SRichard in "2.9.1 Thread-Safety" defines that all functions specified in the 42*6e566bc5SRichard standard are thread-safe except a predefined list of thread-unsafe 43*6e566bc5SRichard functions. 44*6e566bc5SRichard 45*6e566bc5SRichard Glibc defines some of them as thread-safe (e.g. dirname(3)), but adds 46*6e566bc5SRichard non-POSIX thread-unsafe ones (e.g. getopt_long(3)). Glibc's list is 47*6e566bc5SRichard compiled from GNU web documentation with a search for MT-Safe tag: 48*6e566bc5SRichard https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html 49*6e566bc5SRichard 50*6e566bc5SRichard If you want to identify thread-unsafe API for at least one libc or 51*6e566bc5SRichard unsure which libc will be used, use `any` (default). 52*6e566bc5SRichard 53