| .. title:: clang-tidy - concurrency-mt-unsafe |
| |
| 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(); |
| yield(); |
| netent = getnetent(); |
| |
| |
| Examples: |
| |
| .. 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 |
| functions. |
| |
| 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: |
| https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html |
| |
| If you want to identify thread-unsafe API for at least one libc or |
| unsure which libc will be used, use `any` (default). |
| |