[Libreoffice-commits] core.git: include/vcl vcl/win

[Mike Kaganski (via logerrit)]

 include/vcl/svapp.hxx           |   20 ++++++++++++++++++++
 vcl/win/dtrans/WinClipboard.cxx |   13 ++++++++-----
 2 files changed, 28 insertions(+), 5 deletions(-)

New commits:
commit c921f9bd64187823af2356d7a8ceb77444c17219
Author:     Mike Kaganski <mike.kaganski at collabora.com>
AuthorDate: Mon Dec 14 10:00:40 2020 +0300
Commit:     Mike Kaganski <mike.kaganski at collabora.com>
CommitDate: Wed Jan 6 12:22:17 2021 +0100

    Release solar mutex before using an apartment-threaded COM object
    
    See https://lists.freedesktop.org/archives/libreoffice/2020-December/086448.html
    for motivation
    
    This partially reverts f5ab8bcbfd20ecce4a358f62ee3f81b8b968a5de.
    Although this change is questionable, it's intended to avoid
    crashes (tdf#139074); a better fix should replace this eventually.
    
    Optionally releasing a lock isn't a good API and might hide other
    bugs, but the better solution to handle all requests in the main
    thread would need an even larger rewrite of the Windows clipboard
    code. It's simply too late for that in this LO release cycle.
    
    Change-Id: I60e847599fe873025c9903b9d6290ed4cdf4a961
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/107669
    Tested-by: Mike Kaganski <mike.kaganski at collabora.com>
    Reviewed-by: Mike Kaganski <mike.kaganski at collabora.com>

diff --git a/include/vcl/svapp.hxx b/include/vcl/svapp.hxx
index bfa92cf88321..fa5702717086 100644
--- a/include/vcl/svapp.hxx
+++ b/include/vcl/svapp.hxx
@@ -1421,6 +1421,26 @@ public:
     ~SolarMutexReleaser() { Application::AcquireSolarMutex( mnReleased ); }
 };
 
+/**
+ A helper class that calls Application::ReleaseSolarMutex() in its constructor
+ *if it was acquired* and restores the mutex in its destructor.
+*/
+class SolarMutexReleaserIfAcquired
+{
+    const sal_uInt32 mnReleased;
+public:
+    SolarMutexReleaserIfAcquired()
+        : mnReleased(
+            Application::GetSolarMutex().IsCurrentThread() ? Application::ReleaseSolarMutex() : 0)
+    {
+    }
+    ~SolarMutexReleaserIfAcquired()
+    {
+        if (mnReleased)
+            Application::AcquireSolarMutex(mnReleased);
+    }
+};
+
 VCL_DLLPUBLIC Application* GetpApp();
 
 // returns true if vcl is already initialized
diff --git a/vcl/win/dtrans/WinClipboard.cxx b/vcl/win/dtrans/WinClipboard.cxx
index 4135b5cef93c..1f49bde99192 100644
--- a/vcl/win/dtrans/WinClipboard.cxx
+++ b/vcl/win/dtrans/WinClipboard.cxx
@@ -92,9 +92,6 @@ CWinClipboard::~CWinClipboard()
 
 uno::Reference<datatransfer::XTransferable> SAL_CALL CWinClipboard::getContents()
 {
-    DBG_TESTSOLARMUTEX();
-    SolarMutexReleaser aReleaser;
-
     osl::MutexGuard aGuard(m_aMutex);
 
     if (rBHelper.bDisposed)
@@ -129,8 +126,14 @@ uno::Reference<datatransfer::XTransferable> SAL_CALL CWinClipboard::getContents(
         // com smart pointer to the IDataObject from clipboard
         IDataObjectPtr pIDo(new CAPNDataObject(pIDataObject));
 
-        // remember pIDo destroys itself due to the smart pointer
-        rClipContent = CDOTransferable::create(m_xContext, pIDo);
+        {
+            // before calling COM methods of an apartment-threaded COM object, release solar mutex
+            // to avoid deadlocking on waiting clipboard thread that would try to acquire it
+            SolarMutexReleaserIfAcquired aReleaser;
+
+            // remember pIDo destroys itself due to the smart pointer
+            rClipContent = CDOTransferable::create(m_xContext, pIDo);
+        }
 
         osl::MutexGuard aGuard2(m_ClipContentMutex);
         m_foreignContent = rClipContent;