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Diffstat (limited to 'gnu/usr.bin/perl/README.threads')
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diff --git a/gnu/usr.bin/perl/README.threads b/gnu/usr.bin/perl/README.threads new file mode 100644 index 00000000000..136b156e7ff --- /dev/null +++ b/gnu/usr.bin/perl/README.threads @@ -0,0 +1,289 @@ +NOTE + +Threading is a highly experimental feature. There are still a +few race conditions that show up under high contention on SMP +machines. Internal implementation is still subject to changes. +It is not recommended for production use at this time. + +Building + +If you want to build with multi-threading support and you are +running one of the following: + + * Linux 2.x (with the LinuxThreads library installed: that's + the linuxthreads and linuxthreads-devel RPMs for RedHat) + + * Digital UNIX 4.x + + * Digital UNIX 3.x (Formerly DEC OSF/1), see additional note below + + * Solaris 2.x for recentish x (2.5 is OK) + + * IRIX 6.2 or newer. 6.2 will require a few os patches. + IMPORTANT: Without patch 2401, a kernel bug in IRIX 6.2 will + cause your machine to panic and crash when running threaded perl. + IRIX 6.3 and up should be OK. See lower down for patch details. + +then you should be able to use + + ./Configure -Dusethreads -des + make + +and ignore the rest of this "Building" section. If it doesn't +work or you are using another platform which you believe supports +POSIX.1c threads then read on. Additional information may be in +a platform-specific "hints" file in the hints/ subdirectory. + +On other platforms that use Configure to build perl, omit the -d +from your ./Configure arguments. For example, use: + + ./Configure -Dusethreads + +When Configure prompts you for ccflags, insert any other arguments in +there that your compiler needs to use POSIX threads. When Configure +prompts you for linking flags, include any flags required for +threading (usually nothing special is required here). Finally, when +COnfigure prompts you for libraries, include any necessary libraries +(e.g. -lpthread). Pay attention to the order of libraries. It is +probably necessary to specify your threading library *before* your +standard C library, e.g. it might be necessary to have -lpthread -lc, +instead of -lc -lpthread. + +Once you have specified all your compiler flags, you can have Configure +accept all the defaults for the remainder of the session by typing &-d +at any Configure prompt. + +Some additional notes (some of these may be obsolete now, other items +may be handled automatically): + +For Digital Unix 4.x: + Add -pthread to ccflags + Add -pthread to ldflags + Add -lpthread -lc_r to lddlflags + + For some reason, the extra includes for pthreads make Digital UNIX + complain fatally about the sbrk() delcaration in perl's malloc.c + so use the native malloc, e.g. sh Configure -Uusemymalloc, or + manually edit your config.sh as follows: + Change usemymalloc to n + Zap mallocobj and mallocsrc (foo='') + Change d_mymalloc to undef + +For Digital Unix 3.x (Formerly DEC OSF/1): + Add -DOLD_PTHREADS_API to ccflags + If compiling with the GNU cc compiler, remove -thread from ccflags + + (The following should be done automatically if you call Configure + with the -Dusethreads option). + Add -lpthread -lmach -lc_r to libs (in the order specified). + +For IRIX: + (This should all be done automatically by the hint file). + Add -lpthread to libs + For IRIX 6.2, you have to have the following patches installed: + 1404 Irix 6.2 Posix 1003.1b man pages + 1645 IRIX 6.2 & 6.3 POSIX header file updates + 2000 Irix 6.2 Posix 1003.1b support modules + 2254 Pthread library fixes + 2401 6.2 all platform kernel rollup + IMPORTANT: Without patch 2401, a kernel bug in IRIX 6.2 will + cause your machine to panic and crash when running threaded perl. + IRIX 6.3 and up should be OK. + + For IRIX 6.3 and 6.4 the pthreads should work out of the box. + Thanks to Hannu Napari <Hannu.Napari@hut.fi> for the IRIX + pthreads patches information. +For AIX: + (This should all be done automatically by the hint file). + Change cc to xlc_r or cc_r. + Add -DNEED_PTHREAD_INIT to ccflags and cppflags + Add -lc_r to libswanted + Change -lc in lddflags to be -lpthread -lc_r -lc + +For Win32: + See README.win32, and the notes at the beginning of win32/Makefile + or win32/makefile.mk. + +Now you can do a + make + + +O/S specific bugs + +Irix 6.2: See the Irix warning above. + +LinuxThreads 0.5 has a bug which can cause file descriptor 0 to be +closed after a fork() leading to many strange symptoms. Version 0.6 +has this fixed but the following patch can be applied to 0.5 for now: + +----------------------------- cut here ----------------------------- +--- linuxthreads-0.5/pthread.c.ORI Mon Oct 6 13:55:50 1997 ++++ linuxthreads-0.5/pthread.c Mon Oct 6 13:57:24 1997 +@@ -312,8 +312,10 @@ + free(pthread_manager_thread_bos); + pthread_manager_thread_bos = pthread_manager_thread_tos = NULL; + /* Close the two ends of the pipe */ +- close(pthread_manager_request); +- close(pthread_manager_reader); ++ if (pthread_manager_request >= 0) { ++ close(pthread_manager_request); ++ close(pthread_manager_reader); ++ } + pthread_manager_request = pthread_manager_reader = -1; + /* Update the pid of the main thread */ + self->p_pid = getpid(); +----------------------------- cut here ----------------------------- + + +Building the Thread extension + +The Thread extension is now part of the main perl distribution tree. +If you did Configure -Dusethreads then it will have been added to +the list of extensions automatically. + +You can try some of the tests with + cd ext/Thread + perl create.t + perl join.t + perl lock.t + perl io.t +etc. +The io one leaves a thread reading from the keyboard on stdin so +as the ping messages appear you can type lines and see them echoed. + +Try running the main perl test suite too. There are known +failures for some of the DBM/DB extensions (if their underlying +libraries were not compiled to be thread-aware). + + +Bugs + +* FAKE_THREADS should produce a working perl but the Thread +extension won't build with it yet. (FAKE_THREADS has not been +tested at all in recent times.) + +* There may still be races where bugs show up under contention. + +* Need to document "lock", Thread.pm, Queue.pm, ... + + +Debugging + +Use the -DS command-line option to turn on debugging of the +multi-threading code. Under Linux, that also turns on a quick +hack I did to grab a bit of extra information from segfaults. +If you have a fancier gdb/threads setup than I do then you'll +have to delete the lines in perl.c which say + #if defined(DEBUGGING) && defined(USE_THREADS) && defined(__linux__) + DEBUG_S(signal(SIGSEGV, (void(*)(int))catch_sigsegv);); + #endif + + +Background + +Some old globals (e.g. stack_sp, op) and some old per-interpreter +variables (e.g. tmps_stack, cxstack) move into struct thread. +All fields of struct thread which derived from original perl +variables have names of the form Tfoo. For example, stack_sp becomes +the field Tstack_sp of struct thread. For those fields which moved +from original perl, thread.h does + #define foo (thr->Tfoo) +This means that all functions in perl which need to use one of these +fields need an (automatic) variable thr which points at the current +thread's struct thread. For pp_foo functions, it is passed around as +an argument, for other functions they do + dTHR; +which declares and initialises thr from thread-specific data +via pthread_getspecific. If a function fails to compile with an +error about "no such variable thr", it probably just needs a dTHR +at the top. + + +Fake threads + +For FAKE_THREADS, thr is a global variable and perl schedules threads +by altering thr in between appropriate ops. The next and prev fields +of struct thread keep all fake threads on a doubly linked list and +the next_run and prev_run fields keep all runnable threads on a +doubly linked list. Mutexes are stubs for FAKE_THREADS. Condition +variables are implemented as a list of waiting threads. + + +Mutexes and condition variables + +The API is via macros MUTEX_{INIT,LOCK,UNLOCK,DESTROY} and +COND_{INIT,WAIT,SIGNAL,BROADCAST,DESTROY}. + +A mutex is only required to be a simple, fast mutex (e.g. it does not +have to be recursive). It is only ever held across very short pieces +of code. Condition variables are only ever signalled/broadcast while +their associated mutex is held. (This constraint simplifies the +implementation of condition variables in certain porting situations.) +For POSIX threads, perl mutexes and condition variables correspond to +POSIX ones. For FAKE_THREADS, mutexes are stubs and condition variables +are implmented as lists of waiting threads. For FAKE_THREADS, a thread +waits on a condition variable by removing itself from the runnable +list, calling SCHEDULE to change thr to the next appropriate +runnable thread and returning op (i.e. the new threads next op). +This means that fake threads can only block while in PP code. +A PP function which contains a COND_WAIT must be prepared to +handle such restarts and can use the field "private" of struct +thread to record its state. For fake threads, COND_SIGNAL and +COND_BROADCAST work by putting back all the threads on the +condition variables list into the run queue. Note that a mutex +must *not* be held while returning from a PP function. + +Perl locks and condition variables are both implemented as a +condpair_t structure, containing a mutex, an "owner" condition +variable, an owner thread field and another condition variable). +The structure is attached by 'm' magic to any SV. pp_lock locks +such an object by waiting on the ownercond condition variable until +the owner field is zero and then setting the owner field to its own +thread pointer. The lock is semantically recursive so if the owner +field already matches the current thread then pp_lock returns +straight away. If the owner field has to be filled in then +unlock_condpair is queued as an end-of-block destructor and +that function zeroes out the owner field and signals the ownercond +condition variable, thus waking up any other thread that wants to +lock it. When used as a condition variable, the condpair is locked +(involving the above wait-for-ownership and setting the owner field) +and the spare condition variable field is used for waiting on. + + +Thread states + + + $t->join +R_JOINABLE ---------------------> R_JOINED >----\ + | \ pthread_join(t) | ^ | + | \ | | join | pthread_join + | \ | | | + | \ | \------/ + | \ | + | \ | + | $t->detach\ pthread_detach | + | _\| | +ends| R_DETACHED ends | unlink + | \ | + | ends \ unlink | + | \ | + | \ | + | \ | + | \ | + | \ | + V join detach _\| V +ZOMBIE ----------------------------> DEAD + pthread_join pthread_detach + and unlink and unlink + + + +Malcolm Beattie +mbeattie@sable.ox.ac.uk +Last updated: 27 November 1997 + +Configure-related info updated 16 July 1998 by +Andy Dougherty <doughera@lafayette.edu> + +Other minor updates 10 Feb 1999 by +Gurusamy Sarathy |