LLThread::currentID() used to return a U32, a distinct unsigned value
incremented by explicitly constructing LLThread or by calling LLThread::
registerThreadID() early in a thread launched by other means. The latter
imposed an unobvious requirement on new code based on std::thread. Using
std::thread::id instead delegates to the compiler/library the problem of
distinguishing threads launched by any means.

Change lots of explicit U32 declarations. Introduce LLThread::id_t typedef to
avoid having to run around fixing uses again if we later revisit this decision.

LLMutex, which stores an LLThread::id_t, wants a distinguished value meaning
NO_THREAD, and had an enum with that name. But as std::thread::id promises
that the default-constructed value is distinct from every valid value,
NO_THREAD becomes unnecessary and goes away.

Because LLMutex now stores LLThread::id_t instead of U32, make llmutex.h
#include "llthread.h" instead of the other way around. This makes LLMutex an
incomplete type within llthread.h, so move LLThread::lockData() and
unlockData() to the .cpp file. Similarly, remove llrefcount.h's #include
"llmutex.h" to break circularity; instead forward-declare LLMutex.

It turns out that a number of source files assumed that #include "llthread.h"
would get the definition for LLMutex. Sprinkle #include "llmutex.h" as needed.

In the SAFE_SSL code in llcorehttp/httpcommon.cpp, there's an ssl_thread_id()
callback that returns an unsigned long to the SSL library. When LLThread::
currentID() was U32, we could simply return that. But std::thread::id is very
deliberately opaque, and can't be reinterpret_cast to unsigned long.
Fortunately it can be hashed because std::hash is specialized with that type.

fixed crash on exit by making LLInstanceTracker iterators use atomic iterator
nesting count for thread safety

SH-2652 WIP -- Add timers to relevant areas, pause render pipeline while occlusion queries from previous frame are still pending and perform texture decode work.

accessed through the static LLThread::tldata().
Currently this object contains two (public) thread-local
objects: a LLAPRRootPool and a LLVolatileAPRPool.

The first is the general memory pool used by this thread
(and this thread alone), while the second is intended
for short lived memory allocations (needed for APR).
The advantages of not mixing those two is that the latter
is used most frequently, and as a result of it's nature
can be destroyed and reconstructed on a "regular" basis.

This patch adds LLAPRPool (completely replacing the old one),
which is a wrapper around apr_pool_t* and has complete
thread-safity checking.

Whenever an apr call requires memory for some resource,
a memory pool in the form of an LLAPRPool object can
be created with the same life-time as this resource;
assuring clean up of the memory no sooner, but also
not much later than the life-time of the resource
that needs the memory.

Many, many function calls and constructors had the
pool parameter simply removed (it is no longer the
concern of the developer, if you don't write code
that actually does an libapr call then you are no
longer bothered with memory pools at all).

However, I kept the notion of short-lived and
long-lived allocations alive (see my remark in
the jira here: https://jira.secondlife.com/browse/STORM-864?focusedCommentId=235356&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-235356
which requires that the LLAPRFile API needs
to allow the user to specify how long they
think a file will stay open. By choosing
'short_lived' as default for the constructor
that immediately opens a file, the number of
instances where this needs to be specified is
drastically reduced however (obviously, any
automatic LLAPRFile is short lived).

***

Addressed Boroondas remarks in https://codereview.secondlife.com/r/99/
regarding (doxygen) comments. This patch effectively only changes comments.

Includes some 'merge' stuff that ended up in llvocache.cpp
(while starting as a bug fix, now only resulting in a cleanup).

***

Added comment 'The use of apr_pool_t is OK here'.

Added this comment on every line where apr_pool_t
is correctly being used.

This should make it easier to spot (future) errors
where someone started to use apr_pool_t; you can
just grep all sources for 'apr_pool_t' and immediately
see where it's being used while LLAPRPool should
have been used.

Note that merging this patch is very easy:
If there are no other uses of apr_pool_t in the code
(one grep) and it compiles, then it will work.

***

Second Merge (needed to remove 'delete mCreationMutex'
from LLImageDecodeThread::~LLImageDecodeThread).

***

Added back #include <apr_pools.h>.

Apparently that is needed on libapr version 1.2.8.,
the version used by Linden Lab, for calls to
apr_queue_*. This is a bug in libapr (we also
include <apr_queue.h>, that is fixed in (at least) 1.3.7.

Note that 1.2.8 is VERY old. Even 1.3.x is old.

***

License fixes (GPL -> LGPL). And typo in comments.
Addresses merov's comments on the review board.

***

Added Merov's compile fixes for windows.

fix for EXT-5683: viewer crashes at llcommon/llworkerthread.cpp(323): ERROR: LLWorkerClass::checkWork: ASSERT(workreq).

Ok, finally got this to a point where it doesn't break the build and I can check
in. llcommon can be built as a shared library (disabled but can be enabled with
cmake cache var LLCOMMON_LINK_SHARED.

reviewed by Mani on tuesday (I still need to get his suggested changes
re-reviewed)

Merge of QAR-1267 to trunk.  This was a combo merge of QAR-1175 (maint-render-9) and QAR-1236 (dll-msvcrt-2)

svn merge -r 109838:112264 svn+ssh://svn.lindenlab.com/svn/linden/branches/maint-render/maint-render-9-merge-r109833

Result of svn merge -r107256:107258 svn+ssh://svn/svn/user/phoenix/license_2009_merge into trunk. QAR-1165

QAR-648   1.20 Viewer RC10
merge Branch_1-20-Viewer-2 -r 88724:90511 -> release

Result of svn merge -r71162:71205 svn+ssh://svn/svn/linden/branches/new-license into release. only changes files which are not deployed or the comments section of code.