In general, it's assumed that the library initialization function (if initialization isn't delayed) and the library finalization function are run in some thread-safe fashion, with no other parts of the library in question in use. (If dlopen or dlsym in one thread starts running the initializer, and then dlopen/dlsym in another thread returns and lets you start accessing functions or data in the library before the initializer is finished, that really seems like a dlopen/dlsym bug.) It's also assumed that if library A depends on library B, then library B's initializer runs first, and its finalizer last, whether loading dynamically at run time or at process startup/exit. (It appears that AIX 4.3.3 may violate this, at least when we use gcc's constructor/destructor attributes in shared libraries.) Support for freeing the heap storage allocated by a library has NOT, in general, been written. There are hooks, but often they ignore some of the library's local storage, mutexes, etc. If shared library finalization code doesn't get run at all at dlclose time, or if we can't use it because the execution order is wrong, then you'll get memory leaks. Deal with it. Several debugging variables that are not part of our official API are not protected by mutexes. In general, the only way to set them is by changing the sources and recompiling, which obviously has no run-time thread safety issues, or by stopping the process under a debugger, which we blithely assert is "safe enough". Debug code that we don't normally enable may be less thread safe than might be desired. For example, multiple printf calls may be made, with the assumption that the output will not be intermixed with output from some other thread. Offhand, I'm not aware of any cases where debugging code is "really" unsafe, as in likely to crash the program or produce insecure results. Various libraries may call assert() and abort(). This should only be for "can't happen" cases, and indicate programming errors. In some cases, the compiler may be able to infer that the "can't happen" cases really can't happen, and drop the calls, but in many cases, this is not possible. There are cases (e.g., in the com_err library) where errors arising when dealing with other errors are handled by calling abort, for lack of anything better. We should probably clean those up someday. Various libraries call getenv(). This is perfectly safe, as long as nothing is calling setenv or putenv or what have you, while multiple threads are executing. Of course, that severely curtails the ability to control our libraries through that "interface". Various libraries call the ctype functions/macros (isupper, etc). It is assumed that the program does not call setlocale, or does so only while the program is still single-threaded or while calls into the Kerberos libraries are not in progress. The Windows thread safety support is unfinished. I'm assuming that structure fields that are never written to (e.g., after a structure has been initialized and *then* made possibly visible to multiple threads) are safe to read from one thread while another field is being updated by another thread. If that's not the case, some more work is needed (and I'd like details on why it's not safe). ---------------- libcom_err Issues: The callback hook support (set_com_err_hook, reset_com_err_hook, and calls to com_err and com_err_va) uses a mutex to protect the handle on the hook function. As a side effect of this, if a callback function is registered which pops up a window and waits for the users' acknowledgement, then other errors cannot be reported by other threads until after the acknowledgement. This could be fixed with multiple-reader-one-writer type locks, but that's a bit more complicated. The string returned by error_message may be per-thread storage. It can be passed off between threads, but it shouldn't be in use by any thread by the time the originating thread calls error_message again. Error tables must no longer be in use (including pointers returned by error_message) when the library containing them is unloaded. Temporary: A flag variable has been created in error_message.c which is used to try to catch cases where remove_error_table is called after the library finalization function. This generally indicates out-of-order execution of the library finalization functions. The handling of this flag is not thread-safe, but if the finalization function is called, other threads should in theory be finished with this library anyways. Statics: error_message.c, com_err.c, covered above. ---------------- libprofile (and its use in libkrb5) Does no checks to see if it's opened multiple instances of the same file under different names. Does not guard against trying to open a file while another thread or process is in the process of replacing it, or two threads trying to update a file at the same time. The former should be pretty safe on UNIX with atomic rename, but on Windows there's a race condition; there's a window (so to speak) where the filename does not correspond to an actual file. Statics: prof_file.c, a list of opened config files and their parse trees, and a mutex to protect it. ---------------- libk5crypto Uses of the Yarrow code from the krb5 crypto interface are protected by a single mutex. Initialization of the Yarrow state will be done once, the first time these routines are called. Calls directly to the Yarrow functions are not protected. Uses ctype macros; what happens if the locale is changed in a multi-threaded program? Debug var in pbkdf2.c. Statics: pbkdf2.c: debug variable. Statics: prng.c: Global Yarrow data and mutex. Statics: crypto_libinit.c: library initializer aux data. ---------------- libkrb5 (TBD) Uses: ctype macros Uses: getaddrinfo, getnameinfo. According to current specifications, getaddrinfo should be thread-safe; some implementations are not, and we're not attempting to figure out which ones. NetBSD 1.6, for example, had an unsafe implementation. Uses: res_ninit, res_nsearch. If these aren't available, the non-'n' versions will be used, and they are sometimes not thread-safe. Uses: mkstemp, mktemp -- Are these, or our uses of them, likely to be thread-safe? Uses: sigaction The use of sigaction is in the code prompting for a password; we try to catch the keyboard interrupt character being used and turn it into an error return from that function. THIS IS NOT THREAD-SAFE. Uses: tcgetattr, tcsetattr. This is also in the password-prompting code. These are fine as long as no other threads are accessing the same terminal at the same time. Uses: fopen. This is thread-safe, actually, but a multi-threaded server is likely to be using lots of file descriptors. On 32-bit Solaris platforms, fopen will not work if the next available file descriptor number is 256 or higher. This can cause the keytab code to fail. Statics: prompter.c: interrupt flag Statics: ccdefops.c: default operations table pointer Statics: ktdefname.c: variable to override default keytab name, NO LOCKING. DON'T TOUCH THESE VARIABLES, at least in threaded programs. Statics: conv_creds.c: debug variable Statics: sendto_kdc.c: debug variable, in export list for KDC Statics: parse.c: default realm cache, changed to not cache Statics: krb5_libinit.c: lib init aux data Statics: osconfig.c: various internal variables, probably should be const Statics: init_ctx.c: "brand" string; not written. Statics: cc_memory.c: list of caches, with mutex. Statics: c_ustime.c: last timestamp, to implement "microseconds must always increment" Statics: ktbase.c, ccbase.c, rc_base.c: type registries and mutexes. ---------------- libgssapi_krb5 (TBD) Uses: ctype macros Statics: acquire_cred.c: name of keytab to use, and mutex. Statics: gssapi_krb5.c: Statics: init_sec_context.c: Statics: set_ccache.c: Statics: gssapi_generic.c: OID definitions, non-const by specification. We probably could make them const anyways. The keytab name saved away by krb5_gss_register_acceptor_identity is global and protected by a mutex; the ccache name stored by gss_krb5_ccache_name is per-thread. This inconsistency is due to the anticipated usage patterns. The old ccache name returned by gss_krb5_ccache_name if the last parameter is not a null pointer is also stored per-thread, and will be discarded at the next call to that routine from the same thread, or at thread termination. Needs work: check various objects for thread safety ---------------- libkrb4 libdes425 I don't think we're likely to bother with these. Part of the krb4 API requires keeping some internal storage across calls. ---------------- libgssrpc New version is in place. Ignore it for now? ---------------- libkadm5* libkdb5 Skip these for now. We may want the KDC libraries to be thread-safe eventually, so the KDC can take better advantage of hyperthreaded or multiprocessor systems. ---------------- libapputils libpty libss Used by single-threaded programs only (but see above re KDC). Don't bother for now.