comphelper: fix MSVC hang in ThreadPool::shutdown()

Commit aa68c99d88fd7abe08c4aee5206c859a0cdba38e added some code using
std::condition_variable to comphelper.

Built with MSVC 2017, this causes many cppunittester.exe processes to
deadlock in ThreadPool::shutdown():

    maTasksChanged.notify_all();

This ultimately calls NtReleaseKeyedEvent(), which never returns.

The reason appears to be a bug in Windows 7, for which a "hotfix"[1] is
avaiable here, but it's apparently not distributed via Windows Update
so we likely can't rely on users or even developers having this installed.

However, the documentation of DllMain[2] and ExitProcess[3] indicates
that during shutdown, by the time global destructors are invoked
all threads other than the one that called ExitProcess have already
been terminated.

Returning from main() implicitly calls ExitProcess [4].

As it turns out the problem only happens for some CppUnitTests because
soffice.bin will call ThreadPool::shutdown() from Desktop::doShutdown()
while it is still safe.

[1] http://support.microsoft.com/kb/2582203
[2] https://msdn.microsoft.com/en-US/library/windows/desktop/ms682583(v=vs.85).aspx
[3] https://msdn.microsoft.com/en-us/library/windows/desktop/ms682658(v=vs.85).aspx
[4] https://blogs.msdn.microsoft.com/oldnewthing/20100827-00/?p=13023

Change-Id: I6137461ca7efe9a5fbe4f8f8478fb96de3570469
Reviewed-on: https://gerrit.libreoffice.org/35066
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/comphelper/source/misc/threadpool.cxx b/comphelper/source/misc/threadpool.cxx
index 712009d8a2b4..1219ef24b986 100644
--- a/comphelper/source/misc/threadpool.cxx
+++ b/comphelper/source/misc/threadpool.cxx
@@ -89,7 +89,12 @@ ThreadPool::ThreadPool( sal_Int32 nWorkers ) :
 
 ThreadPool::~ThreadPool()
 {
-    shutdown();
+    // note: calling shutdown from global variable dtor blocks forever on Win7
+    // note2: there isn't enough MSVCRT left on exit to call assert() properly
+    // so these asserts just print something to stderr but exit status is
+    // still 0, but hopefully they will be more helpful on non-WNT platforms
+    assert(mbTerminate);
+    assert(maTasks.empty());
 }
 
 struct ThreadPoolStatic : public rtl::StaticWithInit< std::shared_ptr< ThreadPool >,
@@ -127,6 +132,7 @@ sal_Int32 ThreadPool::getPreferredConcurrency()
     return ThreadCount;
 }
 
+// FIXME: what does "this" refer to in the following?
 // FIXME: there should be no need for this as/when our baseline
 // is >VS2015 and drop WinXP; the sorry details are here:
 // https://connect.microsoft.com/VisualStudio/feedback/details/1282596