diff --git a/gcc/objc/THREADS b/gcc/objc/THREADS new file mode 100644 index 0000000000000000000000000000000000000000..f94a2076502c3040d1d0be31db8bfc4f69f4fc99 --- /dev/null +++ b/gcc/objc/THREADS @@ -0,0 +1,206 @@ +This file describes in little detail the modifications to the +Objective-C runtime needed to make it thread safe. + +First off, kudos to Galen Hunt who is the author of this great work. + +If you have an comments or just want to know where to +send me money to express your undying graditude for threading the +Objective-C runtime you can reach Galen at: + + gchunt@cs.rochester.edu + +Any questions, comments, bug reports, etc. should send email either to the +GCC bug account or to: + + Scott Christley <scottc@ocbi.com> + +****************************************************************************** +* Simple test program: + +A simple test program can be found in the thread-test directory. + +****************************************************************************** +* Sarray Threading: + +The most critical component of the Objective-C runtime is the sparse array +structure (sarray). Sarrays store object selectors and implementations. +Following in the tradition of the Objective-C runtime, my threading +support assumes that fast message dispatching is far more important +than *ANY* and *ALL* other operations. The message dispatching thus +uses *NO* locks on any kind. In fact, if you look in sarray.h, you +will notice that the message dispatching has not been modified. +Instead, I have modified the sarray management functions so that all +updates to the sarray data structure can be made in parallel will +message dispatching. + +To support concurrent message dispatching, no dynamically allocated +sarray data structures are freed while more than one thread is +operational. Sarray data structures that are no longer in use are +kept in a linked list of garbage and are released whenever the program +is operating with a single thread. The programmer can also flush the +garbage list by calling sarray_remove_garbage when the programmer can +ensure that no message dispatching is taking place concurrently. The +amount of un-reclaimed sarray garbage should normally be extremely +small in a real program as sarray structures are freed only when using +the "poseAs" functionality and early in program initialization, which +normally occurs while the program is single threaded. + +****************************************************************************** +* Static Variables: + +The following variables are either statically or globally defined. This list +does not include variables which are internal to implementation dependent +versions of thread-*.c. + +The following threading designations are used: + SAFE : Implicitly thread safe. + SINGLE : Must only be used in single thread mode. + MUTEX : Protected by single global mutex objc_runtime_mutex. + UNUSED : Not used in the runtime. + +Variable Name: Usage: Defined: Also used in: +=========================== ====== ============ ===================== +__objc_class_hash MUTEX class.c +__objc_class_links_resolved UNUSED class.c runtime.h +__objc_class_number MUTEX class.c +__objc_dangling_categories UNUSED init.c +__objc_module_list MUTEX init.c +__objc_selector_array MUTEX selector.c +__objc_selector_hash MUTEX selector.c +__objc_selector_max_index MUTEX selector.c sendmsg.c runtime.h +__objc_selector_names MUTEX selector.c +__objc_thread_exit_status SAFE thread.c +__objc_uninstalled_dtable MUTEX sendmsg.c selector.c +_objc_load_callback SAFE init.c objc-api.h +_objc_lookup_class SAFE class.c objc-api.h +_objc_object_alloc SINGLE objects.c objc-api.h +_objc_object_copy SINGLE objects.c objc-api.h +_objc_object_dispose SINGLE objects.c objc-api.h +frwd_sel SAFE2 sendmsg.c +idxsize MUTEX sarray.c sendmsg.c sarray.h +initialize_sel SAFE2 sendmsg.c +narrays MUTEX sarray.c sendmsg.c sarray.h +nbuckets MUTEX sarray.c sendmsg.c sarray.h +nindices MUTEX sarray.c sarray.h +previous_constructors SAFE1 init.c +proto_class SAFE1 init.c +unclaimed_categories MUTEX init.c +unclaimed_proto_list MUTEX init.c +uninitialized_statics MUTEX init.c + +Notes: +1) Initialized once in unithread mode. +2) Initialized value will always be same, guaranteed by lock on selector + hash table. + +****************************************************************************** +* Linking: + +On Solaris, you must link with -lthread to include the system +thread library. We use its low level thread and mutex implementations. + +On OSF/1, you must link with -lpthreads to include the pthreads library. + +On WIN32, thread support is built-in to the WIN32 API; refer to your +compiler documentation for the appropriate library. + +****************************************************************************** +* Threads: + +The thread system attempts to create multiple threads using whatever +operating system or library thread support is available. It does +assume that all system functions are thread safe. Notably this means +that the system implementation of malloc and free must be thread safe. +If a system has multiple processors, the threads are configured for +full parallel processing. + +__objc_init_thread_system(void), int + Initialize the thread subsystem. Call once by __objc_exec_class. + +__objc_fini_thread_system(void), int + Closes the thread subsystem. + +objc_thread_detach(SEL selector, id object, id argument), int + Creates and detaches a new thread. The new thread starts by + sending the given selector with a single argument to the + given object. + +objc_thread_set_priority(int priority), int + Sets a threads relative priority within the program. Valid + options are: + + OBJC_THREAD_INTERACTIVE_PRIORITY + OBJC_THREAD_BACKGROUND_PRIORITY + OBJC_THREAD_LOW_PRIORITY + +objc_thread_get_priority(void), int + Query a threads priority. + +objc_thread_yield(void), void + Yields processor to another thread with equal or higher + priority. It is up to the system scheduler to determine if + the processor is taken or not. + +objc_thread_exit(void), int + Terminates a thread. If this is the last thread executing + then the program will terminate. + +objc_thread_id(void), int + Returns the current thread's id. + +objc_thread_set_data(void *value), int + Set a pointer to the thread's local storage. Local storage is + thread specific. + +objc_thread_get_data(void), void * + Returns the pointer to the thread's local storage. + +****************************************************************************** +* Mutexs: + +Mutexs can be locked recursively. Each mutex locked mutex remembers +its owner (by thread id) and how many times it has been locked. The +last unlock on a mutex removes the system lock and allows other +threads to access the mutex. + +objc_mutex_allocate(void), Mutex_t + Allocates a new mutex. Mutex is initially unlocked. + +objc_mutex_deallocate(Mutex_t mutex), int + Free a mutex. Before freeing the mutex, makes sure that no + one else is using it. + +objc_mutex_lock(Mutex_t mutex), int + Locks a mutex. As mentioned earlier, the same thread may call + this routine repeatedly. + +objc_mutex_trylock(Mutex_t mutex), int + Attempts to lock a mutex. Returns -1 if failed. If lock on + mutex can be acquired then function operates exactly as + objc_mutex_lock. + +objc_mutex_unlock(Mutex_t mutex), int + Unlocks the mutex by one level. Other threads may not acquire + the mutex until this thread has released all locks on it. + +****************************************************************************** +* Sample run of thread-test/checks/test01.m + +<< program started >> -- Program started +__objc_exec_class(Object.m) -- Initialize once +__objc_init_mutex_system +__objc_init_thread_system +__objc_init_selector_tables() +__objc_init_class_tables() +__objc_init_dispatch_tables() +__objc_exec_class(Protocol.m) -- Called repeatedly +__objc_init_protocols(0x000746d4) -- Called repeatedly +class_add_method_list(0x74718, 0x74208) -- Called repeatedly +<< main called >> -- Main called +__objc_init_install_dtable(0x6d980, 0x6d5c0) -- Called repeatedly +<< delegatePool filled, count=10 >> -- Code in secondary function +__objc_init_install_dtable(0x76268, 0x70614) -- Called repeatedly +Array: count=1 -- More secondary code. +EltNodeCollector: count=1 +<< end of program >> -- End of program +