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