[v3 PATCH 1/2] dwrite: Protect cached fontface list when accessed from multiple threads

[Sebastian Lackner]

On 10.08.2017 08:45, Nikolay Sivov wrote:
> Based on patch by Anton Romanov <theli.ua at gmail.com>
> 
> Signed-off-by: Nikolay Sivov <nsivov at codeweavers.com>
> ---
>  dlls/dwrite/dwrite_private.h |  6 ++++--
>  dlls/dwrite/font.c           | 24 ++++++++++++---------
>  dlls/dwrite/main.c           | 50 +++++++++++++++++++++++++++++++++-----------
>  3 files changed, 56 insertions(+), 24 deletions(-)
> 

Isn't it also necessary to protect factory_cache_fontface()?

By the way: An alternative method to implement proper synchronization (which does
not require locking critical sections before InterlockedDecrement) would be to do
something like:

In the destructor:

--- snip ---
    if (!ref)
    {
        EnterCriticalSection(...);
        list_remove(...);
        LeaveCriticalSection(...);

        ...
    }
--- snip ---

And when querying cached font faces:

--- snip ---
    EnterCriticalSection(...);
    LIST_FOR_EACH_ENTRY(...)
    {
        ...

        /* the following code could also be hidden in QueryInterface */
        if (InterlockedIncrement( &obj->refcount ) == 1)
        {
            InterlockedDecrement( &obj->refcount );
            continue;
        }

        /* return it */
    }
    LeaveCriticalSection(...);
--- snip ---

This is also what is done in Wines threadpool implementation [1], and has the
advantage that the CS is not needed for every Release, only when the object is
really destroyed. But in the end it is a matter of taste, for rpcrt4 Jacek
also picked the "hold CS during InterlockedDecrement" method.

[1] https://source.winehq.org/git/wine.git/blob/HEAD:/dlls/ntdll/threadpool.c#l2564

Best regards,
Sebastian