Check for the SQLite mutex API in configure

An SQLite built with SQLITE_THREADSAFE=0, such as the Emscripten port,
does not export sqlite3_mutex_enter(), sqlite3_mutex_try() or
sqlite3_mutex_leave().

Author: gpshead

Modules/_sqlite/util.h

@@ -73,19 +73,28 @@ pysqlite_set_ref(PyObject *owner, PyObject **field, PyObject *value)
 static inline void
 pysqlite_mutex_enter(sqlite3_mutex *mutex)
 {
+#ifdef PY_SQLITE_HAVE_MUTEX
     if (mutex != NULL && sqlite3_mutex_try(mutex) != SQLITE_OK) {
         Py_BEGIN_ALLOW_THREADS
         sqlite3_mutex_enter(mutex);
         Py_END_ALLOW_THREADS
     }
+#else
+    /* An SQLite built without mutexes cannot be in serialized mode. */
+    (void)mutex;
+#endif
 }
 
 static inline void
 pysqlite_mutex_leave(sqlite3_mutex *mutex)
 {
+#ifdef PY_SQLITE_HAVE_MUTEX
     if (mutex != NULL) {
         sqlite3_mutex_leave(mutex);
     }
+#else
+    (void)mutex;
+#endif
 }
 
 static inline void

PCbuild/_sqlite3.vcxproj

@@ -94,7 +94,7 @@
   <ItemDefinitionGroup>
     <ClCompile>
       <AdditionalIncludeDirectories>$(sqlite3Dir);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-      <PreprocessorDefinitions>PY_SQLITE_HAVE_SERIALIZE;PY_SQLITE_ENABLE_LOAD_EXTENSION;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>PY_SQLITE_HAVE_MUTEX;PY_SQLITE_HAVE_SERIALIZE;PY_SQLITE_ENABLE_LOAD_EXTENSION;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemGroup>

configure

@@ -4846,6 +4846,12 @@ dnl hence CPPFLAGS instead of CFLAGS.
           [Define if SQLite was compiled with the serialize API]
         )
       ])
+      AC_CHECK_LIB([sqlite3], [sqlite3_mutex_try], [
+        AC_DEFINE(
+          [PY_SQLITE_HAVE_MUTEX], [1],
+          [Define if SQLite was compiled with mutexes (SQLITE_THREADSAFE != 0)]
+        )
+      ])
     ], [
       have_supported_sqlite3=no
     ])

configure.ac

@@ -1812,6 +1812,9 @@
 /* Define to 1 to build the sqlite module with loadable extensions support. */
 #undef PY_SQLITE_ENABLE_LOAD_EXTENSION
 
+/* Define if SQLite was compiled with mutexes (SQLITE_THREADSAFE != 0) */
+#undef PY_SQLITE_HAVE_MUTEX
+
 /* Define if SQLite was compiled with the serialize API */
 #undef PY_SQLITE_HAVE_SERIALIZE