Add support for sqlite3_unlock_notify

Author: typeless

callback.c

@@ -0,0 +1,5 @@
+void _unlock_notify_callback(void *arg, int argc)
+{
+  extern void unlock_notify_callback(void *, int);
+  unlock_notify_callback(arg, argc);
+}

callback.go

@@ -20,6 +20,8 @@ package sqlite3
 
 void _sqlite3_result_text(sqlite3_context* ctx, const char* s);
 void _sqlite3_result_blob(sqlite3_context* ctx, const void* b, int l);
+
+void _unlock_notify_callback(void *arg, int argc);
 */
 import "C"
 
@@ -362,3 +364,35 @@ func callbackSyntheticForTests(v reflect.Value, err error) callbackArgConverter
 		return v, err
 	}
 }
+
+type unlockNotification struct {
+	notify chan struct{}
+	lock   sync.Mutex
+}
+
+//export unlock_notify_callback
+func unlock_notify_callback(pargv unsafe.Pointer, argc C.int) {
+	argv := *(*uintptr)(pargv)
+	v := (*[1 << 30]uintptr)(unsafe.Pointer(argv))
+	for i := 0; i < int(argc); i++ {
+		un := lookupHandle(v[i]).(unlockNotification)
+		un.notify <- struct{}{}
+	}
+}
+
+var notifyMutex sync.Mutex
+
+//export unlock_notify_wait
+func unlock_notify_wait(db *C.sqlite3) C.int {
+	var un unlockNotification
+
+	un.notify = make(chan struct{})
+	defer close(un.notify)
+
+	argv := [1]uintptr{newHandle(nil, un)}
+	if rv := C.sqlite3_unlock_notify(db, (*[0]byte)(C._unlock_notify_callback), unsafe.Pointer(&argv)); rv != C.SQLITE_OK {
+		return rv
+	}
+	<-un.notify
+	return C.SQLITE_OK
+}

sqlite3.go

@@ -21,6 +21,7 @@ package sqlite3
 #cgo CFLAGS: -DSQLITE_DISABLE_INTRINSIC
 #cgo CFLAGS: -DSQLITE_DEFAULT_WAL_SYNCHRONOUS=1
 #cgo CFLAGS: -DSQLITE_ENABLE_UPDATE_DELETE_LIMIT
+#cgo CFLAGS: -DSQLITE_ENABLE_UNLOCK_NOTIFY
 #cgo CFLAGS: -Wno-deprecated-declarations
 #cgo linux,!android CFLAGS: -DHAVE_PREAD64=1 -DHAVE_PWRITE64=1
 #ifndef USE_LIBSQLITE3
@@ -81,8 +82,25 @@ _sqlite3_exec(sqlite3* db, const char* pcmd, long long* rowid, long long* change
 static int
 _sqlite3_step(sqlite3_stmt* stmt, long long* rowid, long long* changes)
 {
-  int rv = sqlite3_step(stmt);
+  extern int unlock_notify_wait(sqlite3 *db);
+  int rv;
   sqlite3* db = sqlite3_db_handle(stmt);
+
+  for (;;) {
+    rv = sqlite3_step(stmt);
+    if (rv!=SQLITE_LOCKED) {
+      break;
+    }
+    if (sqlite3_extended_errcode(db)!=SQLITE_LOCKED_SHAREDCACHE) {
+      break;
+    }
+    rv = unlock_notify_wait(db);
+    if (rv != SQLITE_OK) {
+      break;
+    }
+    sqlite3_reset(stmt);
+  }
+
   *rowid = (long long) sqlite3_last_insert_rowid(db);
   *changes = (long long) sqlite3_changes(db);
   return rv;
@@ -1399,7 +1417,20 @@ func (c *SQLiteConn) prepare(ctx context.Context, query string) (driver.Stmt, er
 	defer C.free(unsafe.Pointer(pquery))
 	var s *C.sqlite3_stmt
 	var tail *C.char
-	rv := C.sqlite3_prepare_v2(c.db, pquery, -1, &s, &tail)
+	var rv C.int
+	for {
+		rv = C.sqlite3_prepare_v2(c.db, pquery, -1, &s, &tail)
+		if rv == C.SQLITE_OK {
+			break
+		} else if rv == C.SQLITE_LOCKED {
+			rv = unlock_notify_wait(c.db)
+			if rv != C.SQLITE_OK {
+				break
+			}
+		} else {
+			break
+		}
+	}
 	if rv != C.SQLITE_OK {
 		return nil, c.lastError()
 	}