[vlc-devel] [PATCH 2/3] win32: Add a vlc_mta_holder
Hugo Beauzée-Luyssen
hugo at beauzee.fr
Wed Jun 14 14:34:24 CEST 2017
This small helper will hold on to the MTA to ensure it won't be
destroyed between two calls to CoInitializeEx.
This will help us not leaking our TA configurations to libvlc/libvlccore
threads
--
Changes since previous patch #5:
- Use VLC_VAR_COMPARE_EXCHANGE to fix invalid static mutex
Changes since previous patch #4:
- Use a semaphore instead of a wait cond to signal the MTA has been acquired
- Fix mta_holder structure cleanup
Changes since previous patch #3:
- Fix a race condition causing the MTA to potentially not be acquired by
the time vlc_mta_acquire releases.
Changes since previous patch #2:
- Don't use a VLC_OBJECT
- Use static inline functions instead of exported ones
Changes since previous patch:
- Fix potential race condition
- Do not export the functions on !_WIN32
---
src/Makefile.am | 2 +-
src/win32/mta_holder.h | 164 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 165 insertions(+), 1 deletion(-)
create mode 100644 src/win32/mta_holder.h
diff --git a/src/Makefile.am b/src/Makefile.am
index 5f3726c3e6..51062532ca 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -467,7 +467,7 @@ libvlccore_la_LDFLAGS = \
libvlccore_la_DEPENDENCIES = libvlccore.sym
if HAVE_WIN32
libvlccore_la_DEPENDENCIES += libvlc_win32_rc.$(OBJEXT)
-libvlccore_la_LDFLAGS += -Wl,libvlc_win32_rc.$(OBJEXT) -avoid-version -Wc,-static
+libvlccore_la_LDFLAGS += -Wl,libvlc_win32_rc.$(OBJEXT) -avoid-version -Wc,-static $(LIBCOM)
endif
if HAVE_OS2
libvlccore_la_LDFLAGS += -avoid-version
diff --git a/src/win32/mta_holder.h b/src/win32/mta_holder.h
new file mode 100644
index 0000000000..d818dc2d43
--- /dev/null
+++ b/src/win32/mta_holder.h
@@ -0,0 +1,164 @@
+/*****************************************************************************
+ * mta_holder.c: Hold a MTA from another thread
+ *****************************************************************************
+ * Copyright (C) 2002-2017 the VideoLAN and AUTHORS
+ *
+ * Author: Hugo Beauzée-Luyssen <hugo at beauzee.fr>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifndef MTA_HOLDER_H
+# define MTA_HOLDER_H
+
+#include <vlc_common.h>
+#include <vlc_atomic.h>
+
+#include <assert.h>
+#include <windows.h>
+#include <objbase.h>
+
+#ifdef __cplusplus
+using std::atomic_uint;
+#endif
+
+typedef struct vlc_mta_holder
+{
+ vlc_thread_t thread;
+ vlc_mutex_t lock;
+ vlc_sem_t sem;
+ vlc_cond_t ready_cond;
+ bool b_ready;
+ atomic_uint i_refcount;
+} vlc_mta_holder;
+
+static inline void* MtaMainLoop( void* opaque )
+{
+ vlc_mta_holder* p_mta = (vlc_mta_holder*)opaque;
+ CoInitializeEx( NULL, COINIT_MULTITHREADED );
+
+ vlc_mutex_lock( &p_mta->lock );
+ p_mta->b_ready = true;
+ vlc_cond_signal( &p_mta->ready_cond );
+ vlc_mutex_unlock( &p_mta->lock );
+
+ vlc_sem_wait( &p_mta->sem );
+
+ CoUninitialize();
+ return NULL;
+}
+
+/**
+ * Ensure an MTA context will be available until vlc_mta_release gets called.
+ *
+ * In the background, this will create a thread that does nothing but to keep the MTA
+ * refcount greater than 0.
+ *
+ * This is usefull in order not to commit a thread to a specific concurrency model.
+ * This function is win32 specific.
+ */
+static inline vlc_mta_holder* vlc_mta_acquire( vlc_object_t *p_parent )
+{
+ vlc_mta_holder* p_mta = (vlc_mta_holder*)var_CreateGetAddress( p_parent->obj.libvlc, "mta-holder" );
+
+ bool force_var_change = false;
+ if ( p_mta != NULL )
+ {
+ if( atomic_fetch_add( &p_mta->i_refcount, 1u ) == 0 )
+ {
+ /* The mta struct is being destroyed but the var is still present */
+ force_var_change = true;
+ }
+ else
+ goto wait_ready;
+ }
+
+ p_mta = (vlc_mta_holder*) malloc( sizeof( *p_mta ) );
+ if ( unlikely( p_mta == NULL ) )
+ return NULL;
+
+ vlc_mutex_init( &p_mta->lock );
+ vlc_sem_init( &p_mta->sem, 0 );
+ vlc_cond_init( &p_mta->ready_cond );
+ atomic_init( &p_mta->i_refcount, 1u );
+ p_mta->b_ready = false;
+
+ if( force_var_change )
+ var_SetAddress( p_parent->obj.libvlc, "mta-holder", p_mta );
+ else
+ {
+ vlc_value_t newval = { .p_address = p_mta }, oldval = { .p_address = NULL };
+
+ if( var_Change( p_parent->obj.libvlc, "mta-holder", VLC_VAR_COMPARE_EXCHANGE,
+ &oldval, &newval) != VLC_SUCCESS )
+ {
+ /* Worse case scenario: mta is already being initialized by an
+ * other thread, try again */
+
+ vlc_sem_destroy( &p_mta->sem );
+ vlc_cond_destroy( &p_mta->ready_cond );
+ vlc_mutex_destroy( &p_mta->lock );
+ free( p_mta );
+
+ /* It's OK to do a recursive call here: the variable is now created
+ * by an other thread, therefore the next call won't go through
+ * this code path */
+ return vlc_mta_acquire( p_parent );
+ }
+ }
+ if ( vlc_clone( &p_mta->thread, MtaMainLoop, p_mta, VLC_THREAD_PRIORITY_LOW ) )
+ {
+ vlc_sem_destroy( &p_mta->sem );
+ vlc_cond_destroy( &p_mta->ready_cond );
+ vlc_mutex_destroy( &p_mta->lock );
+ free( p_mta );
+ return NULL;
+ }
+
+wait_ready:
+ vlc_mutex_lock( &p_mta->lock );
+ while( !p_mta->b_ready )
+ vlc_cond_wait( &p_mta->ready_cond, &p_mta->lock );
+ vlc_mutex_unlock( &p_mta->lock );
+
+ return p_mta;
+}
+
+/**
+ * Releases a reference to the MTA holder.
+ *
+ * When its refcount reaches 0, the thread created by
+ */
+static inline void vlc_mta_release( vlc_object_t* p_parent )
+{
+ vlc_mta_holder *p_mta = (vlc_mta_holder*)var_GetAddress( p_parent->obj.libvlc, "mta-holder" );
+ assert( p_mta != NULL );
+ if ( atomic_fetch_sub( &p_mta->i_refcount, 1u ) == 1 )
+ {
+ vlc_value_t newval = { .p_address = NULL }, oldval = { .p_address = p_mta };
+ var_Change( p_parent->obj.libvlc, "mta-holder", VLC_VAR_COMPARE_EXCHANGE,
+ &oldval, &newval);
+
+ vlc_sem_post( &p_mta->sem );
+ vlc_join( p_mta->thread, NULL );
+
+ vlc_sem_destroy( &p_mta->sem );
+ vlc_cond_destroy( &p_mta->ready_cond );
+ vlc_mutex_destroy( &p_mta->lock );
+ free( p_mta );
+ }
+}
+
+#endif
--
2.11.0
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