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337 lines
13 KiB
Plaintext
NOTE: This documentation describes the style of threading that was
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available in 5.005. Perl v5.6 also has the early beginnings of
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interpreter-based threads support (which is what will be enabled by
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default when you simply ask for -Dusethreads). However, be advised
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that interpreter threads cannot as yet be created from the Perl level
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yet. If you're looking to create threads from within Perl, chances
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are you _don't_ want interpreter threads, but want the older support
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for threads described below, enabled with:
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sh Configure -Dusethreads -Duse5005threads
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The rest of this document only applies to the use5005threads style of
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threads.
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---------------------------------------------------------------------------
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Support for threading is still in the highly experimental stages. There
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are known race conditions that show up under high contention on SMP
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machines. Internal implementation is still subject to changes.
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It is not recommended for production use at this time.
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---------------------------------------------------------------------------
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Building
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If your system is in the following list you should be able to just:
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./Configure -Dusethreads -Duse5005threads -des
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make
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and ignore the rest of this "Building" section. If not, continue
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from the "Problems" section.
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* Linux 2.* (with the LinuxThreads library installed:
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that's the linuxthreads and linuxthreads-devel RPMs
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for RedHat)
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* Tru64 UNIX (formerly Digital UNIX formerly DEC OSF/1)
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(see additional note below)
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* Solaris 2.* for recentish x (2.5 is OK)
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* IRIX 6.2 or newer. 6.2 will require a few OS patches.
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IMPORTANT: Without patch 2401 (or its replacement),
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a kernel bug in IRIX 6.2 will cause your machine to
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panic and crash when running threaded perl.
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IRIX 6.3 and up should be OK. See lower down for patch details.
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* AIX 4.1.5 or newer.
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* FreeBSD 2.2.8 or newer.
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* OpenBSD
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* NeXTstep, OpenStep
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* OS/2
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* DOS DJGPP
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* VM/ESA
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---------------------------------------------------------------------------
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Problems
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If the simple way doesn't work or you are using another platform which
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you believe supports POSIX.1c threads then read on. Additional
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information may be in a platform-specific "hints" file in the hints/
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subdirectory.
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On platforms that use Configure to build perl, omit the -d from your
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./Configure arguments. For example, use:
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./Configure -Dusethreads -Duse5005threads
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When Configure prompts you for ccflags, insert any other arguments in
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there that your compiler needs to use POSIX threads (-D_REENTRANT,
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-pthreads, -threads, -pthread, -thread, are good guesses). When
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Configure prompts you for linking flags, include any flags required
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for threading (usually nothing special is required here). Finally,
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when Configure prompts you for libraries, include any necessary
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libraries (e.g. -lpthread). Pay attention to the order of libraries.
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It is probably necessary to specify your threading library *before*
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your standard C library, e.g. it might be necessary to have -lpthread
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-lc, instead of -lc -lpthread. You may also need to use -lc_r instead
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of -lc.
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Once you have specified all your compiler flags, you can have Configure
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accept all the defaults for the remainder of the session by typing &-d
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at any Configure prompt.
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Some additional notes (some of these may be obsolete now, other items
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may be handled automatically):
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For Digital Unix 4.x:
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Add -pthread to ccflags
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Add -pthread to ldflags
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Add -lpthread -lc_r to lddlflags
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For some reason, the extra includes for pthreads make Digital UNIX
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complain fatally about the sbrk() delcaration in perl's malloc.c
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so use the native malloc, e.g. sh Configure -Uusemymalloc, or
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manually edit your config.sh as follows:
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Change usemymalloc to n
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Zap mallocobj and mallocsrc (foo='')
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Change d_mymalloc to undef
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For Digital Unix 3.x (Formerly DEC OSF/1):
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Add -DOLD_PTHREADS_API to ccflags
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If compiling with the GNU cc compiler, remove -threads from ccflags
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(The following should be done automatically if you call Configure
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with the -Dusethreads option).
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Add -lpthread -lmach -lc_r to libs (in the order specified).
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For IRIX:
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(This should all be done automatically by the hint file).
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Add -lpthread to libs
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For IRIX 6.2, you have to have the following patches installed:
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1404 Irix 6.2 Posix 1003.1b man pages
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1645 IRIX 6.2 & 6.3 POSIX header file updates
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2000 Irix 6.2 Posix 1003.1b support modules
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2254 Pthread library fixes
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2401 6.2 all platform kernel rollup
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IMPORTANT: Without patch 2401, a kernel bug in IRIX 6.2 will
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cause your machine to panic and crash when running threaded perl.
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IRIX 6.3 and up should be OK.
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For IRIX 6.3 and 6.4 the pthreads should work out of the box.
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Thanks to Hannu Napari <Hannu.Napari@hut.fi> for the IRIX
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pthreads patches information.
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For AIX:
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(This should all be done automatically by the hint file).
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Change cc to xlc_r or cc_r.
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Add -DNEED_PTHREAD_INIT to ccflags and cppflags
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Add -lc_r to libswanted
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Change -lc in lddflags to be -lpthread -lc_r -lc
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For Win32:
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See README.win32, and the notes at the beginning of win32/Makefile
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or win32/makefile.mk.
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Now you can do a
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make
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When you succeed in compiling and testing ("make test" after your
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build) a threaded Perl in a platform previosuly unknown to support
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threaded perl, please let perlbug@perl.com know about your victory.
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Explain what you did in painful detail.
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---------------------------------------------------------------------------
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O/S specific bugs
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Irix 6.2: See the Irix warning above.
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LinuxThreads 0.5 has a bug which can cause file descriptor 0 to be
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closed after a fork() leading to many strange symptoms. Version 0.6
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has this fixed but the following patch can be applied to 0.5 for now:
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----------------------------- cut here -----------------------------
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--- linuxthreads-0.5/pthread.c.ORI Mon Oct 6 13:55:50 1997
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+++ linuxthreads-0.5/pthread.c Mon Oct 6 13:57:24 1997
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@@ -312,8 +312,10 @@
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free(pthread_manager_thread_bos);
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pthread_manager_thread_bos = pthread_manager_thread_tos = NULL;
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/* Close the two ends of the pipe */
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- close(pthread_manager_request);
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- close(pthread_manager_reader);
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+ if (pthread_manager_request >= 0) {
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+ close(pthread_manager_request);
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+ close(pthread_manager_reader);
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+ }
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pthread_manager_request = pthread_manager_reader = -1;
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/* Update the pid of the main thread */
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self->p_pid = getpid();
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----------------------------- cut here -----------------------------
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Building the Thread extension
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The Thread extension is now part of the main perl distribution tree.
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If you did Configure -Dusethreads -Duse5005threads then it will have been
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added to the list of extensions automatically.
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You can try some of the tests with
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cd ext/Thread
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perl create.t
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perl join.t
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perl lock.t
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perl io.t
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etc.
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The io one leaves a thread reading from the keyboard on stdin so
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as the ping messages appear you can type lines and see them echoed.
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Try running the main perl test suite too. There are known
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failures for some of the DBM/DB extensions (if their underlying
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libraries were not compiled to be thread-aware).
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---------------------------------------------------------------------------
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Bugs
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* FAKE_THREADS should produce a working perl but the Thread
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extension won't build with it yet. (FAKE_THREADS has not been
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tested at all in recent times.)
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* There may still be races where bugs show up under contention.
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---------------------------------------------------------------------------
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Debugging
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Use the -DS command-line option to turn on debugging of the
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multi-threading code. Under Linux, that also turns on a quick
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hack I did to grab a bit of extra information from segfaults.
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If you have a fancier gdb/threads setup than I do then you'll
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have to delete the lines in perl.c which say
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#if defined(DEBUGGING) && defined(USE_THREADS) && defined(__linux__)
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DEBUG_S(signal(SIGSEGV, (void(*)(int))catch_sigsegv););
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#endif
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---------------------------------------------------------------------------
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Background
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Some old globals (e.g. stack_sp, op) and some old per-interpreter
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variables (e.g. tmps_stack, cxstack) move into struct thread.
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All fields of struct thread which derived from original perl
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variables have names of the form Tfoo. For example, stack_sp becomes
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the field Tstack_sp of struct thread. For those fields which moved
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from original perl, thread.h does
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#define foo (thr->Tfoo)
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This means that all functions in perl which need to use one of these
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fields need an (automatic) variable thr which points at the current
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thread's struct thread. For pp_foo functions, it is passed around as
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an argument, for other functions they do
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dTHR;
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which declares and initialises thr from thread-specific data
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via pthread_getspecific. If a function fails to compile with an
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error about "no such variable thr", it probably just needs a dTHR
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at the top.
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Fake threads
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For FAKE_THREADS, thr is a global variable and perl schedules threads
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by altering thr in between appropriate ops. The next and prev fields
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of struct thread keep all fake threads on a doubly linked list and
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the next_run and prev_run fields keep all runnable threads on a
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doubly linked list. Mutexes are stubs for FAKE_THREADS. Condition
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variables are implemented as a list of waiting threads.
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Mutexes and condition variables
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The API is via macros MUTEX_{INIT,LOCK,UNLOCK,DESTROY} and
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COND_{INIT,WAIT,SIGNAL,BROADCAST,DESTROY}.
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A mutex is only required to be a simple, fast mutex (e.g. it does not
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have to be recursive). It is only ever held across very short pieces
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of code. Condition variables are only ever signalled/broadcast while
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their associated mutex is held. (This constraint simplifies the
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implementation of condition variables in certain porting situations.)
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For POSIX threads, perl mutexes and condition variables correspond to
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POSIX ones. For FAKE_THREADS, mutexes are stubs and condition variables
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are implmented as lists of waiting threads. For FAKE_THREADS, a thread
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waits on a condition variable by removing itself from the runnable
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list, calling SCHEDULE to change thr to the next appropriate
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runnable thread and returning op (i.e. the new threads next op).
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This means that fake threads can only block while in PP code.
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A PP function which contains a COND_WAIT must be prepared to
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handle such restarts and can use the field "private" of struct
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thread to record its state. For fake threads, COND_SIGNAL and
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COND_BROADCAST work by putting back all the threads on the
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condition variables list into the run queue. Note that a mutex
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must *not* be held while returning from a PP function.
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Perl locks and condition variables are both implemented as a
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condpair_t structure, containing a mutex, an "owner" condition
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variable, an owner thread field and another condition variable).
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The structure is attached by 'm' magic to any SV. pp_lock locks
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such an object by waiting on the ownercond condition variable until
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the owner field is zero and then setting the owner field to its own
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thread pointer. The lock is semantically recursive so if the owner
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field already matches the current thread then pp_lock returns
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straight away. If the owner field has to be filled in then
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unlock_condpair is queued as an end-of-block destructor and
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that function zeroes out the owner field and signals the ownercond
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condition variable, thus waking up any other thread that wants to
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lock it. When used as a condition variable, the condpair is locked
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(involving the above wait-for-ownership and setting the owner field)
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and the spare condition variable field is used for waiting on.
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Thread states
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$t->join
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R_JOINABLE ---------------------> R_JOINED >----\
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| \ pthread_join(t) | ^ |
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| \ | | join | pthread_join
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| \ | | |
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| \ | \------/
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| \ |
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| \ |
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| $t->detach\ pthread_detach |
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| _\| |
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ends| R_DETACHED ends | unlink
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| \ |
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| ends \ unlink |
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| \ |
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| \ |
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| \ |
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| \ |
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V join detach _\| V
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ZOMBIE ----------------------------> DEAD
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pthread_join pthread_detach
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and unlink and unlink
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Malcolm Beattie
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mbeattie@sable.ox.ac.uk
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Last updated: 27 November 1997
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Configure-related info updated 16 July 1998 by
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Andy Dougherty <doughera@lafayette.edu>
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Other minor updates 10 Feb 1999 by
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Gurusamy Sarathy
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More platforms added 26 Jul 1999 by
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Jarkko Hietaniemi
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