GitLab

The first phase of this tidyup is focussed on the header files, and in
particular making sure we are exposinng publicly exactly what we need
to, and no more.

 - Rts.h now includes everything that the RTS exposes publicly,
   rather than a random subset of it.

 - Most of the public header files have moved into subdirectories, and
   many of them have been renamed.  But clients should not need to
   include any of the other headers directly, just #include the main
   public headers: Rts.h, HsFFI.h, RtsAPI.h.

 - All the headers needed for via-C compilation have moved into the
   stg subdirectory, which is self-contained.  Most of the headers for
   the rest of the RTS APIs have moved into the rts subdirectory.

 - I left MachDeps.h where it is, because it is so widely used in
   Haskell code.
 
 - I left a deprecated stub for RtsFlags.h in place.  The flag
   structures are now exposed by Rts.h.

 - Various internal APIs are no longer exposed by public header files.

 - Various bits of dead code and declarations have been removed

 - More gcc warnings are turned on, and the RTS code is more
   warning-clean.

 - More source files #include "PosixSource.h", and hence only use
   standard POSIX (1003.1c-1995) interfaces.

There is a lot more tidying up still to do, this is just the first
pass.  I also intend to standardise the names for external RTS APIs
(e.g use the rts_ prefix consistently), and declare the internal APIs
as hidden for shared libraries.

Similarly to the way we save errno across context switches and
suspendThread/resumeThread, we must save and restore the Win32 error
code via GetLastError()/SetLastError().  Fixes #896.

So that we can build the RTS with the NCG.

This patch makes throwTo work with -threaded, and also refactors large
parts of the concurrency support in the RTS to clean things up.  We
have some new files:

  RaiseAsync.{c,h}	asynchronous exception support
  Threads.{c,h}         general threading-related utils

Some of the contents of these new files used to be in Schedule.c,
which is smaller and cleaner as a result of the split.

Asynchronous exception support in the presence of multiple running
Haskell threads is rather tricky.  In fact, to my annoyance there are
still one or two bugs to track down, but the majority of the tests run
now.

Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.

The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level.  The build system now makes no
pretense at being multi-project, it is just the GHC build system.

No doubt this will break many things, and there will be a period of
instability while we fix the dependencies.  A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.

This gives some control over affinity, while we figure out the best
way to automatically schedule threads to make best use of the
available parallelism.

In addition to the primitive, there is also:
 
  GHC.Conc.forkOnIO :: Int -> IO () -> IO ThreadId

where 'forkOnIO i m' creates a thread on Capability (i `rem` N), where
N is the number of available Capabilities set by +RTS -N.

Threads forked by forkOnIO do not automatically migrate when there are
free Capabilities, like normal threads do.  Still, if you're using
forkOnIO exclusively, it's a good idea to do +RTS -qm to disable work
pushing anyway (work pushing takes too much time when the run queues
are large, this is something we need to fix).

There are two new options in the -threaded RTS:
 
  -qm       Don't automatically migrate threads between CPUs
  -qw       Migrate a thread to the current CPU when it is woken up

previously both of these were effectively off, i.e. threads were
migrated between CPUs willy-milly, and threads were always migrated to
the current CPU when woken up.  This is the first step in tweaking the
scheduling for more effective work balancing, there will no doubt be
more to come.

Along the lines of the clean/dirty arrays and IORefs implemented
recently, now threads are marked clean or dirty depending on whether
they need to be scanned during a minor GC or not.  This should speed
up GC when there are lots of threads, especially if most of them are
idle.

Big re-hash of the threaded/SMP runtime

This is a significant reworking of the threaded and SMP parts of
the runtime.  There are two overall goals here:

  - To push down the scheduler lock, reducing contention and allowing
    more parts of the system to run without locks.  In particular,
    the scheduler does not require a lock any more in the common case.

  - To improve affinity, so that running Haskell threads stick to the
    same OS threads as much as possible.

At this point we have the basic structure working, but there are some
pieces missing.  I believe it's reasonably stable - the important
parts of the testsuite pass in all the (normal,threaded,SMP) ways.

In more detail:

  - Each capability now has a run queue, instead of one global run
    queue.  The Capability and Task APIs have been completely
    rewritten; see Capability.h and Task.h for the details.

  - Each capability has its own pool of worker Tasks.  Hence, Haskell
    threads on a Capability's run queue will run on the same worker
    Task(s).  As long as the OS is doing something reasonable, this
    should mean they usually stick to the same CPU.  Another way to
    look at this is that we're assuming each Capability is associated
    with a fixed CPU.

  - What used to be StgMainThread is now part of the Task structure.
    Every OS thread in the runtime has an associated Task, and it
    can ask for its current Task at any time with myTask().

  - removed RTS_SUPPORTS_THREADS symbol, use THREADED_RTS instead
    (it is now defined for SMP too).

  - The RtsAPI has had to change; we must explicitly pass a Capability
    around now.  The previous interface assumed some global state.
    SchedAPI has also changed a lot.

  - The OSThreads API now supports thread-local storage, used to
    implement myTask(), although it could be done more efficiently
    using gcc's __thread extension when available.

  - I've moved some POSIX-specific stuff into the posix subdirectory,
    moving in the direction of separating out platform-specific
    implementations.

  - lots of lock-debugging and assertions in the runtime.  In particular,
    when DEBUG is on, we catch multiple ACQUIRE_LOCK()s, and there is
    also an ASSERT_LOCK_HELD() call.

What's missing so far:

  - I have almost certainly broken the Win32 build, will fix soon.

  - any kind of thread migration or load balancing.  This is high up
    the agenda, though.

  - various performance tweaks to do

  - throwTo and forkProcess still do not work in SMP mode

[mingw only]
Better handling of I/O request abortions upon throwing an exception
to a Haskell thread. As was, a thread blocked on an I/O request was
simply unblocked, but its corresponding worker thread wasn't notified
that the request had been abandoned.

This manifested itself in GHCi upon Ctrl-C being hit at the prompt -- the
worker thread blocked waiting for input on stdin prior to Ctrl-C would
stick around even though its corresponding Haskell thread had been
thrown an Interrupted exception. The upshot was that the worker would
consume the next character typed in after Ctrl-C, but then just dropping
it. Dealing with this turned out to be even more interesting due to
Win32 aborting any console reads when Ctrl-C/Break events are delivered.

The story could be improved upon (at the cost of portability) by making
the Scheduler able to abort worker thread system calls; as is, requests
are cooperatively abandoned. Maybe later.

Also included are other minor tidyups to Ctrl-C handling under mingw.

Merge to STABLE.

- Now that labels are always prefixed with '&' in .hc code, we have to
  fix some sloppiness in the RTS .cmm code.  Fortunately it's not too
  painful.

- SMP: acquire/release the storage manager lock around
  atomicModifyMutVar#.  This is a hack: atomicModifyMutVar# isn't
  atomic under SMP otherwise, but the SM lock is a large sledgehammer.
  I think I'll apply the sledgehammer to the MVar primitives too, for
  the time being.

* Some preprocessors don't like the C99/C++ '//' comments after a
  directive, so use '/* */' instead. For consistency, a lot of '//' in
  the include files were converted, too.

* UnDOSified libraries/base/cbits/runProcess.c.

* My favourite sport: Killed $Id$s.

GC changes: instead of threading old-generation mutable lists
through objects in the heap, keep it in a separate flat array.

This has some advantages:

  - the IND_OLDGEN object is now only 2 words, so the minimum
    size of a THUNK is now 2 words instead of 3.  This saves
    some amount of allocation (about 2% on average according to
    my measurements), and is more friendly to the cache by
    squashing objects together more.

  - keeping the mutable list separate from the IND object
    will be necessary for our multiprocessor implementation.

  - removing the mut_link field makes the layout of some objects
    more uniform, leading to less complexity and special cases.

  - I also unified the two mutable lists (mut_once_list and mut_list)
    into a single mutable list, which lead to more simplifications
    in the GC.

Rationalise the BUILD,HOST,TARGET defines.

Recall that:

  - build is the platform we're building on
  - host is the platform we're running on
  - target is the platform we're generating code for

The change is that now we take these definitions as applying from the
point of view of the particular source code being built, rather than
the point of view of the whole build tree.

For example, in RTS and library code, we were previously testing the
TARGET platform.  But under the new rule, the platform on which this
code is going to run is the HOST platform.  TARGET only makes sense in
the compiler sources.

In practical terms, this means that the values of BUILD, HOST & TARGET
may vary depending on which part of the build tree we are in.

Actual changes:

 - new file: includes/ghcplatform.h contains platform defines for
   the RTS and library code.

 - new file: includes/ghcautoconf.h contains the autoconf settings
   only (HAVE_BLAH).  This is so that we can get hold of these
   settings independently of the platform defines when necessary
   (eg. in GHC).

 - ghcconfig.h now #includes both ghcplatform.h and ghcautoconf.h.

 - MachRegs.h, which is included into both the compiler and the RTS,
   now has to cope with the fact that it might need to test either
   _TARGET_ or _HOST_ depending on the context.

 - the compiler's Makefile now generates
     stage{1,2,3}/ghc_boot_platform.h
   which contains platform defines for the compiler.  These differ
   depending on the stage, of course: in stage2, the HOST is the
   TARGET of stage1.  This was wrong before.

 - The compiler doesn't get platform info from Config.hs any more.
   Previously it did (sometimes), but unless we want to generate
   a new Config.hs for each stage we can't do this.

 - GHC now helpfully defines *_{BUILD,HOST}_{OS,ARCH} automatically
   in CPP'd Haskell source.

 - ghcplatform.h defines *_TARGET_* for backwards compatibility
   (ghcplatform.h is included by ghcconfig.h, which is included by
   config.h, so code which still #includes config.h will get the TARGET
   settings as before).

 - The Users's Guide is updated to mention *_HOST_* rather than
   *_TARGET_*.

 - coding-style.html in the commentary now contains a section on
   platform defines.  There are further doc updates to come.

Thanks to Wolfgang Thaller for pointing me in the right direction.

Support for atomic memory transactions and associated regression tests conc041-048

64-bit fixes.

Don't assume that sizeof(int) == sizeof(StgInt).
This assumption creeped in in many places since 6.2.

Get rid of SUPPORTS_EMPTY_STRUCTS, and just avoid using empty struct
definitions.

Various fixes and removal of dead code.

Merge backend-hacking-branch onto HEAD.  Yay!

Threaded RTS improvements:

  - Make the main_threads list doubly linked.  Have threads
    remove themselves from this list when they complete, rather
    than searching for completed main threads each time around
    the scheduler loop.  This removes an O(n) loop from the
    scheduler, but adds some new constraints (basically completed
    threads must remain on the run queue until dealt with, including
    threads which have been killed by an async exception).

  - Add a pointer from the TSO to the StgMainThread struct, for
    main threads.  This avoids a number of places where we had
    to traverse the list of main threads to find the right one,
    including one place in the scheduler loop.  Adding a field to
    a TSO is cheap.

  - taskStart: we should be resetting the startingWorkerThread flag
    in here.  Not sure why we aren't; maybe this got lost at some point.

  - Use the BlockedOnCCall flags in the non-threaded RTS too.  Q: what
    should happen if a thread does a foreign call which re-enters the
    RTS, and then sends an async exception to the original thread?
    Answer: it should deadlock, which it does in the threaded RTS, and
    this commit makes it do so in the non-threaded RTS too (see
    testsuite/tests/concurrent/should_run/conc040.hs).

Tidy up a couple of unportable coding issues:

- conditionally use empty structs.
- use GNU attributes only if supported.
- 'long long' usage
- use of 'inline' in declarations and definitions.

Upshot of these changes is that MSVC is now capable of compiling
the non-.hc portions of the RTS.

Bound Threads
=============

Introduce a way to use foreign libraries that rely on thread local state
from multiple threads (mainly affects the threaded RTS).

See the file threads.tex in CVS at haskell-report/ffi/threads.tex
(not entirely finished yet) for a definition of this extension. A less formal
description is also found in the documentation of Control.Concurrent.

The changes mostly affect the THREADED_RTS (./configure --enable-threaded-rts),
except for saving & restoring errno on a per-TSO basis, which is also necessary
for the non-threaded RTS (a bugfix).

Detailed list of changes
------------------------

- errno is saved in the TSO object and restored when necessary:
ghc/includes/TSO.h, ghc/rts/Interpreter.c, ghc/rts/Schedule.c

- rts_mainLazyIO is no longer needed, main is no special case anymore
ghc/includes/RtsAPI.h, ghc/rts/RtsAPI.c, ghc/rts/Main.c, ghc/rts/Weak.c

- passCapability: a new function that releases the capability and "passes"
  it to a specific OS thread:
ghc/rts/Capability.h ghc/rts/Capability.c

- waitThread(), scheduleWaitThread() and schedule() get an optional
  Capability *initialCapability passed as an argument:
ghc/includes/SchedAPI.h, ghc/rts/Schedule.c, ghc/rts/RtsAPI.c

- Bound Thread scheduling (that's what this is all about):
ghc/rts/Schedule.h, ghc/rts/Schedule.c

- new Primop isCurrentThreadBound#:
ghc/compiler/prelude/primops.txt.pp, ghc/includes/PrimOps.h, ghc/rts/PrimOps.hc,
ghc/rts/Schedule.h, ghc/rts/Schedule.c

- a simple function, rtsSupportsBoundThreads, that returns true if THREADED_RTS
  is defined:
ghc/rts/Schedule.h, ghc/rts/Schedule.c

- a new implementation of forkProcess (the old implementation stays in place
  for the non-threaded case). Partially broken; works for the standard
  fork-and-exec case, but not for much else. A proper forkProcess is
  really next to impossible to implement:
ghc/rts/Schedule.c

- Library support for bound threads:
    Control.Concurrent.
      rtsSupportsBoundThreads, isCurrentThreadBound, forkOS,
      runInBoundThread, runInUnboundThread
libraries/base/Control/Concurrent.hs, libraries/base/Makefile,
libraries/base/include/HsBase.h, libraries/base/cbits/forkOS.c (new file)

New primop (mingw only),

  asyncDoProc# :: Addr# -> Addr# -> State# RealWorld-> (# State# RealWorld, Int#, Int# #)

which lets a Haskell thread hand off a pointer to external code (1st arg) for
asynchronous execution by the RTS worker thread pool. Second arg is data passed
in to the asynchronous routine. The routine is _not_ permitted to re-enter
the RTS as part of its execution.

Asynchronous / non-blocking I/O for Win32 platforms.

This commit introduces a Concurrent Haskell friendly view of I/O on
Win32 platforms. Through the use of a pool of worker Win32 threads, CH
threads may issue asynchronous I/O requests without blocking the
progress of other CH threads. The issuing CH thread is blocked until
the request has been serviced though.

GHC.Conc exports the primops that take care of issuing the
asynchronous I/O requests, which the IO implementation now takes
advantage of. By default, all Handles are non-blocking/asynchronous,
but should performance become an issue, having a per-Handle flag for
turning off non-blocking could easily be imagined&introduced.

[Incidentally, this thread pool-based implementation could easily be
extended to also allow Haskell code to delegate the execution of
arbitrary pieces of (potentially blocking) external code to another OS
thread. Given how relatively gnarly the locking story has turned out
to be with the 'threaded' RTS, that may not be such a bad idea.]

This commit fixes many bugs and limitations in the threaded RTS.
There are still some issues remaining, though.

The following bugs should have been fixed:

- [+] "safe" calls could cause crashes
- [+] yieldToReturningWorker/grabReturnCapability
    -     It used to deadlock.
- [+] couldn't wake blocked workers
    -     Calls into the RTS could go unanswered for a long time, and
          that includes ordinary callbacks in some circumstances.
- [+] couldn't block on an MVar and expect to be woken up by a signal
      handler
    -     Depending on the exact situation, the RTS shut down or
          blocked forever and ignored the signal.
- [+] The locking scheme in RtsAPI.c didn't work
- [+] run_thread label in wrong place (schedule())
- [+] Deadlock in GHC.Handle
    -     if a signal arrived at the wrong time, an mvar was never
          filled again
- [+] Signals delivered to the "wrong" thread were ignored or handled
      too late.

Issues:
*) If GC can move TSO objects (I don't know - can it?), then ghci
will occasionally crash when calling foreign functions, because the
parameters are stored on the TSO stack.

*) There is still a race condition lurking in the code
(both threaded and non-threaded RTS are affected):
If a signal arrives after the check for pending signals in
schedule(), but before the call to select() in awaitEvent(),
select() will be called anyway. The signal handler will be
executed much later than expected.

*) For Win32, GHC doesn't yet support non-blocking IO, so while a
thread is waiting for IO, no call-ins can happen. If the RTS is
blocked in awaitEvent, it uses a polling loop on Win32, so call-ins
should work (although the polling loop looks ugly).

*) Deadlock detection is disabled for the threaded rts, because I
don't know how to do it properly in the presence of foreign call-ins
from foreign threads.
This causes the tests conc031, conc033 and conc034 to fail.

*) "safe" is currently treated as "threadsafe". Implementing "safe" in
a way that blocks other Haskell threads is more difficult than was
thought at first. I think it could be done with a few additional lines
of code, but personally, I'm strongly in favour of abolishing the
distinction.

*) Running finalizers at program termination is inefficient - there
are two OS threads passing messages back and forth for every finalizer
that is run. Also (just as in the non-threaded case) the finalizers
are run in parallel to any remaining haskell threads and to any
foreign call-ins that might still happen.

Merge the eval-apply-branch on to the HEAD
------------------------------------------

This is a change to GHC's evaluation model in order to ultimately make
GHC more portable and to reduce complexity in some areas.

At some point we'll update the commentary to describe the new state of
the RTS.  Pending that, the highlights of this change are:

  - No more Su.  The Su register is gone, update frames are one
    word smaller.

  - Slow-entry points and arg checks are gone.  Unknown function calls
    are handled by automatically-generated RTS entry points (AutoApply.hc,
    generated by the program in utils/genapply).

  - The stack layout is stricter: there are no "pending arguments" on
    the stack any more, the stack is always strictly a sequence of
    stack frames.

    This means that there's no need for LOOKS_LIKE_GHC_INFO() or
    LOOKS_LIKE_STATIC_CLOSURE() any more, and GHC doesn't need to know
    how to find the boundary between the text and data segments (BIG WIN!).

  - A couple of nasty hacks in the mangler caused by the neet to
    identify closure ptrs vs. info tables have gone away.

  - Info tables are a bit more complicated.  See InfoTables.h for the
    details.

  - As a side effect, GHCi can now deal with polymorphic seq.  Some bugs
    in GHCi which affected primitives and unboxed tuples are now
    fixed.

  - Binary sizes are reduced by about 7% on x86.  Performance is roughly
    similar, some programs get faster while some get slower.  I've seen
    GHCi perform worse on some examples, but haven't investigated
    further yet (GHCi performance *should* be about the same or better
    in theory).

  - Internally the code generator is rather better organised.  I've moved
    info-table generation from the NCG into the main codeGen where it is
    shared with the C back-end; info tables are now emitted as arrays
    of words in both back-ends.  The NCG is one step closer to being able
    to support profiling.

This has all been fairly thoroughly tested, but no doubt I've messed
up the commit in some way.

- Make TSO "stable" again: The thread label was changing the size of the
   TSO if you were building a debugging-RTS, leading to binary
   incompatibility. Now we map TSOs to strings using Hash.c.

- API change for labelThread: Label arbitrary threads.

Two new scheduler-API primops:

1) GHC.Conc.forkProcess/forkProcess# :: IO Int
   This is a low-level call to fork() to replace Posix.forkProcess().
   In a Concurrent Haskell setting, only the thread invoking forkProcess()
   is alive in the child process. Other threads will be GC'ed!
      This brings the RTS closer to pthreads, where a call to fork()
   doesn't clone any pthreads, either.
      The result is 0 for the child and the child's pid for the parent.
   The primop will barf() when used on mingw32, sorry.

2) GHC.Conc.labelThread/forkProcess# :: String -> IO ()
   Useful for scheduler debugging: If the RTS is compiled with DEBUGging
   support, this primitive assigns a name to the current thread which
   will be used in debugging output (+RTS -D1). For larger applications,
   simply numbering threads is not sufficient.
     Notice: The Haskell side of this call is always available, but if
   you are not compiling with debugging support, the actual primop will
   turn into a no-op.

uh, make that the StgTSOBlockReason enum

Add BlockedOnCCall to StgTSOBlockInfo enum

Remove annoying warnings about using a deprecated extension
when compiling via gcc-3.0.

#if __GNUC__ >= 3
/* Assume that a flexible array member at the end of a struct
 * can be defined thus: T arr[]; */
#define FLEXIBLE_ARRAY
#else
/* Assume that it must be defined thus: T arr[0]; */
#define FLEXIBLE_ARRAY 0
#endif

A test program (hsking) compiled fine with gcc-3.0!

Changed comment to reflect reality: We now use 32-bit thread IDs, not
64-bit ones.

Don't cast pointers to ints to perform pointer arithmetic.

-*- outline -*-
Time-stamp: <Thu Mar 22 2001 03:50:16 Stardate: [-30]6365.79 hwloidl>

This commit covers changes in GHC to get GUM (way=mp) and GUM/GdH (way=md)
working. It is a merge of my working version of GUM, based on GHC 4.06,
with GHC 4.11. Almost all changes are in the RTS (see below).

GUM is reasonably stable, we used the 4.06 version in large-ish programs for
recent papers. Couple of things I want to change, but nothing urgent.
GUM/GdH has just been merged and needs more testing. Hope to do that in the
next weeks. It works in our working build but needs tweaking to run.
GranSim doesn't work yet (*sigh*). Most of the code should be in, but needs
more debugging.

ToDo: I still want to make the following minor modifications before the release
- Better wrapper skript for parallel execution [ghc/compiler/main]
- Update parallel docu: started on it but it's minimal [ghc/docs/users_guide]
- Clean up [nofib/parallel]: it's a real mess right now (*sigh*)
- Update visualisation tools (minor things only IIRC) [ghc/utils/parallel]
- Add a Klingon-English glossary

* RTS:

Almost all changes are restricted to ghc/rts/parallel and should not
interfere with the rest. I only comment on changes outside the parallel
dir:

- Several changes in Schedule.c (scheduling loop; createThreads etc);
  should only affect parallel code
- Added ghc/rts/hooks/ShutdownEachPEHook.c
- ghc/rts/Linker.[ch]: GUM doesn't know about Stable Names (ifdefs)!!
- StgMiscClosures.h: END_TSO_QUEUE etc now defined here (from StgMiscClosures.hc)
                     END_ECAF_LIST was missing a leading stg_
- SchedAPI.h: taskStart now defined in here; it's only a wrapper around
              scheduleThread now, but might use some init, shutdown later
- RtsAPI.h: I have nuked the def of rts_evalNothing

* Compiler:

- ghc/compiler/main/DriverState.hs
  added PVM-ish flags to the parallel way
  added new ways for parallel ticky profiling and distributed exec

- ghc/compiler/main/DriverPipeline.hs
  added a fct run_phase_MoveBinary which is called with way=mp after linking;
  it moves the bin file into a PVM dir and produces a wrapper script for
  parallel execution
  maybe cleaner to add a MoveBinary phase in DriverPhases.hs but this way
  it's less intrusive and MoveBinary makes probably only sense for mp anyway

* Nofib:

- nofib/spectral/Makefile, nofib/real/Makefile, ghc/tests/programs/Makefile:
  modified to skip some tests if HWL_NOFIB_HACK is set; only tmp to record
  which test prgs cause problems in my working build right now