SGI Freeware 1999 August

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Text File | 1998-10-28 | 7.4 KB | 265 lines

TTTThhhhrrrreeeeaaaadddd((((3333)))) 22223333////JJJJuuuullll////99998888 ((((ppppeeeerrrrllll 5555....000000005555,,,, ppppaaaattttcccchhhh 00002222)))) TTTThhhhrrrreeeeaaaadddd((((3333)))) NNNNAAAAMMMMEEEE Thread - multithreading SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS use Thread; my $t = new Thread \&start_sub, @start_args; $t->join; my $tid = Thread->self->tid; my $tlist = Thread->list; lock($scalar); use Thread 'async'; use Thread 'eval'; DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN The Thread module provides multithreading support for perl. FFFFUUUUNNNNCCCCTTTTIIIIOOOONNNNSSSS new \&start_sub new \&start_sub, LIST new starts a new thread of execution in the referenced subroutine. The optional list is passed as parameters to the subroutine. Execution continues in both the subroutine and the code after the new call. new Thread returns a thread object representing the newly created thread. lock VARIABLE lock places a lock on a variable until the lock goes out of scope. If the variable is locked by another thread, the lock call will block until it's available. lock is recursive, so multiple calls to lock are safe--the variable will remain locked until the outermost lock on the variable goes out of scope. Locks on variables only affect lock calls--they do _n_o_t affect normal access to a variable. (Locks on subs are different, and covered in a bit) If you really, _r_e_a_l_l_y want locks to block access, then go ahead and tie them to something and manage this yourself. This is done on purpose. While managing Page 1 (printed 10/23/98) TTTThhhhrrrreeeeaaaadddd((((3333)))) 22223333////JJJJuuuullll////99998888 ((((ppppeeeerrrrllll 5555....000000005555,,,, ppppaaaattttcccchhhh 00002222)))) TTTThhhhrrrreeeeaaaadddd((((3333)))) access to variables is a good thing, perl doesn't force you out of its living room... If a container object, such as a hash or array, is locked, all the elements of that container are not locked. For example, if a thread does a lock @a, any other thread doing a lock($a[12]) won't block. You may also lock a sub, using lock &sub. Any calls to that sub from another thread will block until the lock is released. This behaviour is not equvalent to use attrs qw(locked) in the sub. use attrs qw(locked) serializes access to a subroutine, but allows different threads non-simultaneous access. lock &sub, on the other hand, will not allow _a_n_y other thread access for the duration of the lock. Finally, lock will traverse up references exactly _o_n_e level. lock(\$a) is equivalent to lock($a), while lock(\\$a) is not. async BLOCK; async creates a thread to execute the block immediately following it. This block is treated as an anonymous sub, and so must have a semi-colon after the closing brace. Like new Thread, async returns a thread object. Thread->self The Thread->self function returns a thread object that represents the thread making the Thread->self call. Thread->list Thread->list returns a list of thread objects for all running and finished but un-joined threads. cond_wait VARIABLE The cond_wait function takes a lllloooocccckkkkeeeedddd variable as a parameter, unlocks the variable, and blocks until another thread does a cond_signal or cond_broadcast for that same locked variable. The variable that cond_wait blocked on is relocked after the cond_wait is satisfied. If there are multiple threads cond_waiting on the same variable, all but one will reblock waiting to reaquire the lock on the variable. (So if you're only using cond_wait for synchronization, give up the lock as soon as possible) cond_signal VARIABLE The cond_signal function takes a locked variable as Page 2 (printed 10/23/98) TTTThhhhrrrreeeeaaaadddd((((3333)))) 22223333////JJJJuuuullll////99998888 ((((ppppeeeerrrrllll 5555....000000005555,,,, ppppaaaattttcccchhhh 00002222)))) TTTThhhhrrrreeeeaaaadddd((((3333)))) a parameter and unblocks one thread that's cond_waiting on that variable. If more than one thread is blocked in a cond_wait on that variable, only one (and which one is indeterminate) will be unblocked. If there are no threads blocked in a cond_wait on the variable, the signal is discarded. cond_broadcast VARIABLE The cond_broadcast function works similarly to cond_wait. cond_broadcast, though, will unblock aaaallllllll the threads that are blocked in a cond_wait on the locked variable, rather than only one. MMMMEEEETTTTHHHHOOOODDDDSSSS join join waits for a thread to end and returns any values the thread exited with. join will block until the thread has ended, though it won't block if the thread has already terminated. If the thread being joined died, the error it died with will be returned at this time. If you don't want the thread performing the join to die as well, you should either wrap the join in an eval or use the eval thread method instead of join. eval The eval method wraps an eval around a join, and so waits for a thread to exit, passing along any values the thread might have returned. Errors, of course, get placed into $@. tid The tid method returns the tid of a thread. The tid is a monotonically increasing integer assigned when a thread is created. The main thread of a program will have a tid of zero, while subsequent threads will have tids assigned starting with one. LLLLIIIIMMMMIIIITTTTAAAATTTTIIIIOOOONNNNSSSS The sequence number used to assign tids is a simple integer, and no checking is done to make sure the tid isn't currently in use. If a program creates more than 2^32 - 1 threads in a single run, threads may be assigned duplicate tids. This limitation may be lifted in a future version of Perl. SSSSEEEEEEEE AAAALLLLSSSSOOOO the _a_t_t_r_s manpage, the _T_h_r_e_a_d::_Q_u_e_u_e manpage, the _T_h_r_e_a_d::_S_e_m_a_p_h_o_r_e manpage, the _T_h_r_e_a_d::_S_p_e_c_i_f_i_c manpage. Page 3 (printed 10/23/98) TTTThhhhrrrreeeeaaaadddd((((3333)))) 22223333////JJJJuuuullll////99998888 ((((ppppeeeerrrrllll 5555....000000005555,,,, ppppaaaattttcccchhhh 00002222)))) TTTThhhhrrrreeeeaaaadddd((((3333)))) Page 4 (printed 10/23/98)