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Diffstat (limited to 'libobjc/THREADS')
| -rw-r--r-- | libobjc/THREADS | 339 |
1 files changed, 339 insertions, 0 deletions
diff --git a/libobjc/THREADS b/libobjc/THREADS new file mode 100644 index 000000000..5004b2cbc --- /dev/null +++ b/libobjc/THREADS @@ -0,0 +1,339 @@ +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 gratitude 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@net-community.com> + +* 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. + + +****************************************************************************** +* Frontend/Backend design: + +The design of the Objective-C runtime thread and mutex functions utilizes a +frontend/backend implementation. + +The frontend, as characterized by the files thr.h and thr.c, is a set +of platform independent structures and functions which represent the +user interface. For example, objc_mutex_lock(). Objective-C programs +should use these structures and functions for their thread and mutex +work if they wish to maintain a high degree of portability across +platforms. + +The backend is currently GCC's gthread code (gthr.h and related). For +example, __gthread_objc_mutex_lock(). The thread system is +automatically configured when GCC is configured. On most platforms +this thread backend is able to automatically switch to non-multi-threaded +mode if the threading library is not linked in. + +If you want to compile libobjc standalone, then you would need to modify +the configure.in and makefiles for it and you need to import the +gthread code from GCC. + +****************************************************************************** +* 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. + +* Backend initialization functions + +__objc_init_thread_system(void), int + Initialize the thread subsystem. Called once by __objc_exec_class. + Return -1 if error otherwise return 0. + +__objc_close_thread_system(void), int + Closes the thread subsystem, not currently guaranteed to be called. + Return -1 if error otherwise return 0. + +***** +* Frontend thread functions +* User programs should use these functions. + +objc_thread_detach(SEL selector, id object, id argument), objc_thread_t + 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 thread's 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 thread's 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. + +***** +* Backend thread functions +* User programs should *NOT* directly call these functions. + +__gthr_objc_thread_detach(void (*func)(void *arg), void *arg), objc_thread_t + Spawns a new thread executing func, called by objc_thread_detach. + Return NULL if error otherwise return thread id. + +__gthr_objc_thread_set_priority(int priority), int + Set the thread's priority, called by objc_thread_set_priority. + Return -1 if error otherwise return 0. + +__gthr_objc_thread_get_priority(void), int + Query a thread's priority, called by objc_thread_get_priority. + Return -1 if error otherwise return the priority. + +__gthr_objc_thread_yield(void), void + Yields the processor, called by objc_thread_yield. + +__gthr_objc_thread_exit(void), int + Terminates the thread, called by objc_thread_exit. + Return -1 if error otherwise function does not return. + +__gthr_objc_thread_id(void), objc_thread_t + Returns the current thread's id, called by objc_thread_id. + Return -1 if error otherwise return thread id. + +__gthr_objc_thread_set_data(void *value), int + Set pointer for thread local storage, called by objc_thread_set_data. + Returns -1 if error otherwise return 0. + +__gthr_objc_thread_get_data(void), void * + Returns the pointer to the thread's local storage. + Returns NULL if error, called by objc_thread_get_data. + + +****************************************************************************** +* Mutexes: + +Mutexes can be locked recursively. Each 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. + +***** +* Frontend mutex functions +* User programs should use these functions. + +objc_mutex_allocate(void), objc_mutex_t + Allocates a new mutex. Mutex is initially unlocked. + Return NULL if error otherwise return mutex pointer. + +objc_mutex_deallocate(objc_mutex_t mutex), int + Free a mutex. Before freeing the mutex, makes sure that no + one else is using it. + Return -1 if error otherwise return 0. + +objc_mutex_lock(objc_mutex_t mutex), int + Locks a mutex. As mentioned earlier, the same thread may call + this routine repeatedly. + Return -1 if error otherwise return 0. + +objc_mutex_trylock(objc_mutex_t mutex), int + Attempts to lock a mutex. If lock on mutex can be acquired + then function operates exactly as objc_mutex_lock. + Return -1 if failed to acquire lock otherwise return 0. + +objc_mutex_unlock(objc_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. + Return -1 if error otherwise return 0. + +***** +* Backend mutex functions +* User programs should *NOT* directly call these functions. + +__gthr_objc_mutex_allocate(objc_mutex_t mutex), int + Allocates a new mutex, called by objc_mutex_allocate. + Return -1 if error otherwise return 0. + +__gthr_objc_mutex_deallocate(objc_mutex_t mutex), int + Free a mutex, called by objc_mutex_deallocate. + Return -1 if error otherwise return 0. + +__gthr_objc_mutex_lock(objc_mutex_t mutex), int + Locks a mutex, called by objc_mutex_lock. + Return -1 if error otherwise return 0. + +__gthr_objc_mutex_trylock(objc_mutex_t mutex), int + Attempts to lock a mutex, called by objc_mutex_trylock. + Return -1 if failed to acquire lock or error otherwise return 0. + +__gthr_objc_mutex_unlock(objc_mutex_t mutex), int + Unlocks the mutex, called by objc_mutex_unlock. + Return -1 if error otherwise return 0. + +****************************************************************************** +* Condition Mutexes: + +Mutexes can be locked recursively. Each 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. + +* +* Frontend condition mutex functions +* User programs should use these functions. +* + +objc_condition_allocate(void), objc_condition_t + Allocate a condition mutex. + Return NULL if error otherwise return condition pointer. + +objc_condition_deallocate(objc_condition_t condition), int + Deallocate a condition. Note that this includes an implicit + condition_broadcast to insure that waiting threads have the + opportunity to wake. It is legal to dealloc a condition only + if no other thread is/will be using it. Does NOT check for + other threads waiting but just wakes them up. + Return -1 if error otherwise return 0. + +objc_condition_wait(objc_condition_t condition, objc_mutex_t mutex), int + Wait on the condition unlocking the mutex until objc_condition_signal() + or objc_condition_broadcast() are called for the same condition. The + given mutex *must* have the depth 1 so that it can be unlocked + here, for someone else can lock it and signal/broadcast the condition. + The mutex is used to lock access to the shared data that make up the + "condition" predicate. + Return -1 if error otherwise return 0. + +objc_condition_broadcast(objc_condition_t condition), int + Wake up all threads waiting on this condition. It is recommended that + the called would lock the same mutex as the threads in + objc_condition_wait before changing the "condition predicate" + and make this call and unlock it right away after this call. + Return -1 if error otherwise return 0. + +objc_condition_signal(objc_condition_t condition), int + Wake up one thread waiting on this condition. + Return -1 if error otherwise return 0. + +* +* Backend condition mutex functions +* User programs should *NOT* directly call these functions. +* + +__gthr_objc_condition_allocate(objc_condition_t condition), int + Allocate a condition mutex, called by objc_condition_allocate. + Return -1 if error otherwise return 0. + +__gthr_objc_condition_deallocate(objc_condition_t condition), int + Deallocate a condition, called by objc_condition_deallocate. + Return -1 if error otherwise return 0. + +__gthr_objc_condition_wait(objc_condition_t condition, objc_mutex_t mutex), int + Wait on the condition, called by objc_condition_wait. + Return -1 if error otherwise return 0 when condition is met. + +__gthr_objc_condition_broadcast(objc_condition_t condition), int + Wake up all threads waiting on this condition. + Called by objc_condition_broadcast. + Return -1 if error otherwise return 0. + +__gthr_objc_condition_signal(objc_condition_t condition), int + Wake up one thread waiting on this condition. + Called by objc_condition_signal. + Return -1 if error otherwise return 0. |