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In GHC 6.12.x I found a rare deadlock caused by this
lock-order-reversal:

AQ cap->lock
  startWorkerTask
    newTask
      AQ sched_mutex

scheduleCheckBlackHoles
  AQ sched_mutex
   unblockOne_
    wakeupThreadOnCapabilty
      AQ cap->lock

so sched_mutex and cap->lock are taken in a different order in two
places.

This doesn't happen in the HEAD because we don't have
scheduleCheckBlackHoles, but I thought it would be prudent to make
this less likely to happen in the future by using a different mutex in
newTask.  We can clearly see that the all_tasks mutex cannot be
involved in a deadlock, becasue we never call anything else while
holding it.

Now that we are trying to support cross compilation, we can't use
    "$(TARGETPLATFORM)" != "$(HOSTPLATFORM)"
as a test for HC-porting.

Which was being used seemed to be random

As discussed on the libraries/haskell-cafe mailing lists
  http://www.haskell.org/pipermail/libraries/2010-April/013420.html

This is a replacement for block/unblock in the asychronous exceptions
API to fix a problem whereby a function could unblock asynchronous
exceptions even if called within a blocked context.

The new terminology is "mask" rather than "block" (to avoid confusion
due to overloaded meanings of the latter).

In GHC, we changed the names of some primops:

  blockAsyncExceptions#   -> maskAsyncExceptions#
  unblockAsyncExceptions# -> unmaskAsyncExceptions#
  asyncExceptionsBlocked# -> getMaskingState#

and added one new primop:

  maskUninterruptible#

See the accompanying patch to libraries/base for the API changes.

QueryPerformanceCounter() on Windows gives much better resolution than
GetSystemTimeAsFileTime().

To improve performance of the RTS when dynamically linked on x86, I
previously disabled -fPIC for certain critical modules (the GC, and a
few others).  However, build reports suggest that the dynamic linker
on OS X doesn't like this, so I'm disabling this optimsation on that
platform.

Noticed by Henrique Ferreiro <hferreiro@udc.es>, thanks!

Validation fails when validating with PAPI support (i.e. GhcRtsWithPapi  = YES
in validate.mk).  The problem is that the posix symbols are defined by a header
included from papi.h. Compilation then fails because these symbols are
redefined in PosixSource.h. 

This patch adds an undefine for the posix symbols after including papi.h and
before including PosixSource.h. The #undefines are localized to Papi.c since
that is the only case where they are getting defined twice.

And add a comment about the dangers of int overflow

This patch extends the PAPI support in the RTS to allow collection of native
events. PAPI can collect data for native events that are exposed by the
hardware beyond the PAPI present events. The native events supported on your
hardware can found by using the papi_native_avail tool.

The RTS already allows users to specify PAPI preset events from the command
line. This patch extends that support to allow users to specify native events.
The changes needed are:

1) New option (#) for the RTS PAPI flag for native events. For example, to
   collect the native event 0x40000000, use ./a.out +RTS -a#0x40000000 -sstderr

2) Update the PAPI_FLAGS struct to store whether the user specified event is a
   papi preset or a native event

3) Update init_countable_events function to add the native events after parsing
   the event code and decoding the name using PAPI_event_code_to_name

This avoids unnecessary work and potential loss of information

This may not be ideal, but it should get GHC building on all platforms
again.

see comment for details

This lets automatic prefetching work better, for a tiny performance boost

This "if" is inside another "if" which checks for RtsFlags.GcFlags.generations
> 1, so testing this again is redundant, assuming the number of generations
won't change during program execution.

Patch from Barney Stratford

The new strategies library (parallel-2.0+, preferably 2.2+) is now
required for parallel programming, otherwise parallelism will be lost.

Apparently on Solaris it is an error to omit _ISOC99_SOURCE when using
_POSIX_C_SOURCE==200112L.