X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=README.threads;h=89a202e18b10bd72a7d8a6716aa2055baa1103cc;hb=8bb8fffa0cd55f5ec6c1b52236f8c5baff79c3c6;hp=7dae3efbcbecc2f05542ab7409f4932bf8386253;hpb=0f15f207c55ce70f46ebbd3be6c3d54763665084;p=p5sagit%2Fp5-mst-13.2.git diff --git a/README.threads b/README.threads index 7dae3ef..89a202e 100644 --- a/README.threads +++ b/README.threads @@ -1,7 +1,246 @@ +NOTE: This documentation describes the style of threading that was +available in Perl 5.005. Perl 5.6.0 introduced the early beginnings of +interpreter-based threads support, also known as ithreads, and in Perl +5.8.0 the interpeter threads became available from perl level through +the threads and threads::shared modules (in Perl 5.6 ithreads are +available only internally and to XS extension builders, and used +by the Win32 port for emulating fork()). + +If you really want the older support for threads described below, +it is enabled with: + + sh Configure -Dusethreads -Duse5005threads + +Be warned that the old 5.005 implementation of threads is known +to be quite buggy, and unmaintained, which means that the bugs +are there to stay. (We are not mean by not fixing the bugs: +the bugs are just really, really, really hard to fix. Honest.) + +The rest of this document only applies to the use5005threads style of +threads, and the comments on what works on which platform are highly +obsolete and preserved here for archaeology buffs only. The +architecture specific hints files do all the necessary option +tweaking automatically during Configure, both for the 5.005 threads +and for the new interpreter threads. + +--------------------------------------------------------------------------- + +Support for threading is still in the highly experimental stages. There +are known 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 your system is in the following list you should be able to just: + + ./Configure -Dusethreads -Duse5005threads -des + make + +and ignore the rest of this "Building" section. If not, continue +from the "Problems" section. + + * Linux 2.* (with the LinuxThreads library installed: + that's the linuxthreads and linuxthreads-devel RPMs + for RedHat) + + * Tru64 UNIX (formerly Digital UNIX formerly DEC OSF/1) + (see additional note below) + + * Solaris 2.* for recentish x (2.5 is OK) + + * IRIX 6.2 or newer. 6.2 will require a few OS patches. + IMPORTANT: Without patch 2401 (or its replacement), + 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. + + * AIX 4.1.5 or newer. + + * FreeBSD 2.2.8 or newer. + + * OpenBSD + + * NeXTstep, OpenStep + + * OS/2 + + * DOS DJGPP + + * VM/ESA + +--------------------------------------------------------------------------- + +Problems + +If the simple way 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 platforms that use Configure to build perl, omit the -d from your +./Configure arguments. For example, use: + + ./Configure -Dusethreads -Duse5005threads + +When Configure prompts you for ccflags, insert any other arguments in +there that your compiler needs to use POSIX threads (-D_REENTRANT, +-pthreads, -threads, -pthread, -thread, are good guesses). 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. You may also need to use -lc_r instead +of -lc. + +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() declaration 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 -threads 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 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 + +When you succeed in compiling and testing ("make test" after your +build) a threaded Perl in a platform previously unknown to support +threaded perl, please let perlbug@perl.com know about your victory. +Explain what you did in painful detail. + +--------------------------------------------------------------------------- + +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 -Duse5005threads 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. + +--------------------------------------------------------------------------- + +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_5005THREADS) && 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 (apart from a few only applicable to -FAKE_THREADS) are of the form Tfoo. For example, stack_sp becomes +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) @@ -15,6 +254,9 @@ 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 @@ -26,10 +268,16 @@ 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}. 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 +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 implemented 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). @@ -41,12 +289,60 @@ 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 are a condpair_t structure (a triple of a mutex, a -condtion variable and an owner thread field) attached by 'm' -magic to any SV. pp_lock locks such an object by waiting on the -condition variable until the owner field is zero and then setting -the owner field to its own thread pointer. The lock is 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, releasing the lock. +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 + +Other minor updates 10 Feb 1999 by +Gurusamy Sarathy + +More platforms added 26 Jul 1999 by +Jarkko Hietaniemi