1 /* 2 * Copyright (C) 2023 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 //! takes a JavaVM to a static reference. 18 //! 19 //! JavaVM is shared as multiple JavaVM within a single process is not allowed 20 //! per [JNI spec](https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/invocation.html) 21 //! The unique JavaVM need to be shared over (potentially) different threads. 22 23 use std::sync::{Arc, Once}; 24 25 use anyhow::Result; 26 use jni::JavaVM; 27 28 static mut JVM: Option<Arc<JavaVM>> = None; 29 static INIT: Once = Once::new(); 30 /// set_once sets the unique JavaVM that can be then accessed using get_static_ref() 31 /// 32 /// The function shall only be called once. set_once(jvm: JavaVM) -> Result<()>33pub(crate) fn set_once(jvm: JavaVM) -> Result<()> { 34 // Safety: follows [this pattern](https://doc.rust-lang.org/std/sync/struct.Once.html). 35 // Modification to static mut is nested inside call_once. 36 unsafe { 37 INIT.call_once(|| { 38 JVM = Some(Arc::new(jvm)); 39 }); 40 } 41 Ok(()) 42 } 43 /// Gets a 'static reference to the unique JavaVM. Returns None if set_once() was never called. get_static_ref() -> Option<&'static Arc<JavaVM>>44pub(crate) fn get_static_ref() -> Option<&'static Arc<JavaVM>> { 45 // Safety: follows [this pattern](https://doc.rust-lang.org/std/sync/struct.Once.html). 46 // Modification to static mut is nested inside call_once. 47 unsafe { JVM.as_ref() } 48 } 49