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