See:
https://bugs.freedesktop.org/show_bug.cgi?id=8801
http://lists.freedesktop.org/archives/cairo/2006-December/008945.html
diff -ru cairo-1.2.6/src/cairo-cache.c cairo-1.2.6-locking/src/cairo-cache.c
--- cairo-1.2.6/src/cairo-cache.c	2006-11-01 03:27:38.000000000 +0100
+++ cairo-1.2.6-locking/src/cairo-cache.c	2007-01-18 20:23:06.000000000 +0100
@@ -38,6 +38,8 @@
 
 #include "cairoint.h"
 
+CAIRO_MUTEX_DECLARE (cairo_cache_refcount_mutex);
+
 struct _cairo_cache {
     cairo_hash_table_t *hash_table;
 
@@ -188,9 +190,11 @@
 void
 _cairo_cache_freeze (cairo_cache_t *cache)
 {
+    CAIRO_MUTEX_LOCK (cairo_cache_refcount_mutex);
     assert (cache->freeze_count >= 0);
 
     cache->freeze_count++;
+    CAIRO_MUTEX_UNLOCK (cairo_cache_refcount_mutex);
 }
 
 /**
@@ -210,12 +214,14 @@
 void
 _cairo_cache_thaw (cairo_cache_t *cache)
 {
+    CAIRO_MUTEX_LOCK (cairo_cache_refcount_mutex);
     assert (cache->freeze_count > 0);
 
     cache->freeze_count--;
 
     if (cache->freeze_count == 0)
 	_cairo_cache_shrink_to_accomodate (cache, 0);
+    CAIRO_MUTEX_UNLOCK (cairo_cache_refcount_mutex);
 }
 
 /**
@@ -312,16 +318,20 @@
 		     cairo_cache_entry_t *entry)
 {
     cairo_status_t status;
+    CAIRO_MUTEX_LOCK (cairo_cache_refcount_mutex);
 
     _cairo_cache_shrink_to_accomodate (cache, entry->size);
 
     status = _cairo_hash_table_insert (cache->hash_table,
 				       (cairo_hash_entry_t *) entry);
-    if (status)
+    if (status){
+        CAIRO_MUTEX_UNLOCK (cairo_cache_refcount_mutex);
 	return status;
+    }
 
     cache->size += entry->size;
 
+    CAIRO_MUTEX_UNLOCK (cairo_cache_refcount_mutex);
     return CAIRO_STATUS_SUCCESS;
 }
 
@@ -341,6 +351,7 @@
 _cairo_cache_remove (cairo_cache_t	 *cache,
 		     cairo_cache_entry_t *entry)
 {
+    CAIRO_MUTEX_LOCK (cairo_cache_refcount_mutex);
     cache->size -= entry->size;
 
     _cairo_hash_table_remove (cache->hash_table,
@@ -348,6 +359,7 @@
 
     if (cache->entry_destroy)
 	cache->entry_destroy (entry);
+    CAIRO_MUTEX_UNLOCK (cairo_cache_refcount_mutex);
 }
 
 /**
diff -ru cairo-1.2.6/src/cairo-pattern.c cairo-1.2.6-locking/src/cairo-pattern.c
--- cairo-1.2.6/src/cairo-pattern.c	2006-11-02 23:53:40.000000000 +0100
+++ cairo-1.2.6-locking/src/cairo-pattern.c	2007-01-18 20:23:06.000000000 +0100
@@ -29,6 +29,8 @@
 
 #include "cairoint.h"
 
+CAIRO_MUTEX_DECLARE (cairo_pattern_refcount_mutex);
+
 const cairo_solid_pattern_t cairo_pattern_nil = {
     { CAIRO_PATTERN_TYPE_SOLID, 	/* type */
       CAIRO_REF_COUNT_INVALID,		/* ref_count */
@@ -497,13 +499,18 @@
     if (pattern == NULL)
 	return NULL;
 
-    if (pattern->ref_count == CAIRO_REF_COUNT_INVALID)
+    CAIRO_MUTEX_LOCK (cairo_pattern_refcount_mutex);
+
+    if (pattern->ref_count == CAIRO_REF_COUNT_INVALID){
+	CAIRO_MUTEX_UNLOCK (cairo_pattern_refcount_mutex);
 	return pattern;
+    }
 
     assert (pattern->ref_count > 0);
 
     pattern->ref_count++;
 
+    CAIRO_MUTEX_UNLOCK (cairo_pattern_refcount_mutex);
     return pattern;
 }
 slim_hidden_def (cairo_pattern_reference);
@@ -557,17 +564,23 @@
     if (pattern == NULL)
 	return;
 
-    if (pattern->ref_count == CAIRO_REF_COUNT_INVALID)
+    CAIRO_MUTEX_LOCK (cairo_pattern_refcount_mutex);
+    if (pattern->ref_count == CAIRO_REF_COUNT_INVALID){
+	CAIRO_MUTEX_UNLOCK (cairo_pattern_refcount_mutex);
 	return;
+    }
 
     assert (pattern->ref_count > 0);
 
     pattern->ref_count--;
-    if (pattern->ref_count)
+    if (pattern->ref_count){
+	CAIRO_MUTEX_UNLOCK (cairo_pattern_refcount_mutex);
 	return;
+    }
 
     _cairo_pattern_fini (pattern);
     free (pattern);
+    CAIRO_MUTEX_UNLOCK (cairo_pattern_refcount_mutex);
 }
 slim_hidden_def (cairo_pattern_destroy);
 
diff -ru cairo-1.2.6/src/cairo-scaled-font.c cairo-1.2.6-locking/src/cairo-scaled-font.c
--- cairo-1.2.6/src/cairo-scaled-font.c	2006-11-01 03:27:38.000000000 +0100
+++ cairo-1.2.6-locking/src/cairo-scaled-font.c	2007-01-18 20:23:06.000000000 +0100
@@ -906,6 +906,8 @@
     if (scaled_font->status)
 	return scaled_font->status;
 
+    _cairo_scaled_font_freeze_cache (scaled_font);
+
     if (scaled_font->backend->show_glyphs != NULL) {
 	status = scaled_font->backend->show_glyphs (scaled_font,
 						    op, pattern,
@@ -914,16 +916,16 @@
 						    dest_x, dest_y,
 						    width, height,
 						    glyphs, num_glyphs);
-	if (status != CAIRO_INT_STATUS_UNSUPPORTED)
+	if (status != CAIRO_INT_STATUS_UNSUPPORTED){
+	    _cairo_scaled_font_thaw_cache (scaled_font);
 	    return status;
+	}
     }
 
     /* Font display routine either does not exist or failed. */
 
     status = CAIRO_STATUS_SUCCESS;
 
-    _cairo_cache_freeze (scaled_font->glyphs);
-
     for (i = 0; i < num_glyphs; i++) {
 	int x, y;
 	cairo_surface_pattern_t glyph_pattern;
@@ -1005,7 +1007,7 @@
     }
 
 CLEANUP_MASK:
-    _cairo_cache_thaw (scaled_font->glyphs);
+    _cairo_scaled_font_thaw_cache (scaled_font);
 
     if (mask != NULL)
 	cairo_surface_destroy (mask);
diff -ru cairo-1.2.6/src/cairo-surface.c cairo-1.2.6-locking/src/cairo-surface.c
--- cairo-1.2.6/src/cairo-surface.c	2006-11-02 23:53:40.000000000 +0100
+++ cairo-1.2.6-locking/src/cairo-surface.c	2007-01-18 20:23:06.000000000 +0100
@@ -41,6 +41,8 @@
 #include "cairo-surface-fallback-private.h"
 #include "cairo-clip-private.h"
 
+CAIRO_MUTEX_DECLARE (cairo_surface_refcount_mutex);
+
 const cairo_surface_t _cairo_surface_nil = {
     &cairo_image_surface_backend,	/* backend */
     CAIRO_SURFACE_TYPE_IMAGE,
@@ -410,13 +412,18 @@
     if (surface == NULL)
 	return NULL;
 
-    if (surface->ref_count == CAIRO_REF_COUNT_INVALID)
+    CAIRO_MUTEX_LOCK (cairo_surface_refcount_mutex);
+
+    if (surface->ref_count == CAIRO_REF_COUNT_INVALID){
+        CAIRO_MUTEX_UNLOCK (cairo_surface_refcount_mutex);
 	return surface;
+    }
 
     assert (surface->ref_count > 0);
 
     surface->ref_count++;
 
+    CAIRO_MUTEX_UNLOCK (cairo_surface_refcount_mutex);
     return surface;
 }
 slim_hidden_def (cairo_surface_reference);
@@ -435,20 +442,27 @@
     if (surface == NULL)
 	return;
 
-    if (surface->ref_count == CAIRO_REF_COUNT_INVALID)
+    CAIRO_MUTEX_LOCK (cairo_surface_refcount_mutex);
+
+    if (surface->ref_count == CAIRO_REF_COUNT_INVALID){
+        CAIRO_MUTEX_UNLOCK (cairo_surface_refcount_mutex);
 	return;
+    }
 
     assert (surface->ref_count > 0);
 
     surface->ref_count--;
-    if (surface->ref_count)
+    if (surface->ref_count){
+        CAIRO_MUTEX_UNLOCK (cairo_surface_refcount_mutex);
 	return;
+    }
 
     cairo_surface_finish (surface);
 
     _cairo_user_data_array_fini (&surface->user_data);
 
     free (surface);
+    CAIRO_MUTEX_UNLOCK (cairo_surface_refcount_mutex);
 }
 slim_hidden_def(cairo_surface_destroy);
 
diff -ru cairo-1.2.6/src/cairo-win32-surface.c cairo-1.2.6-locking/src/cairo-win32-surface.c
--- cairo-1.2.6/src/cairo-win32-surface.c	2006-11-02 23:53:40.000000000 +0100
+++ cairo-1.2.6-locking/src/cairo-win32-surface.c	2007-01-18 20:24:20.000000000 +0100
@@ -1179,6 +1179,10 @@
 CRITICAL_SECTION cairo_scaled_font_map_mutex;
 CRITICAL_SECTION cairo_ft_unscaled_font_map_mutex;
 
+CRITICAL_SECTION cairo_cache_refcount_mutex;
+CRITICAL_SECTION cairo_pattern_refcount_mutex;
+CRITICAL_SECTION cairo_surface_refcount_mutex;
+
 static int _cairo_win32_initialized = 0;
 
 void
@@ -1191,6 +1195,10 @@
     InitializeCriticalSection (&cairo_scaled_font_map_mutex);
     InitializeCriticalSection (&cairo_ft_unscaled_font_map_mutex);
 
+		InitializeCriticalSection (&cairo_cache_refcount_mutex);
+		InitializeCriticalSection (&cairo_pattern_refcount_mutex);
+		InitializeCriticalSection (&cairo_surface_refcount_mutex);
+
     _cairo_win32_initialized = 1;
 }
 
@@ -1209,6 +1217,9 @@
     DeleteCriticalSection (&cairo_toy_font_face_hash_table_mutex);
     DeleteCriticalSection (&cairo_scaled_font_map_mutex);
     DeleteCriticalSection (&cairo_ft_unscaled_font_map_mutex);
+		DeleteCriticalSection (&cairo_cache_refcount_mutex);
+		DeleteCriticalSection (&cairo_pattern_refcount_mutex);
+		DeleteCriticalSection (&cairo_surface_refcount_mutex);
     break;
   }
   return TRUE;