jni_glue/
vm.rs

1use super::*;
2
3/// FFI: Use **&VM** instead of *const JavaVM.  This represents a global, process-wide Java exection environment.
4/// 
5/// On Android, there is only one VM per-process, although on desktop it's possible (if rare) to have multiple VMs
6/// within the same process.  While this library does not yet support having multiple VMs active simultaniously, please
7/// don't hesitate to [file an issue](https://github.com/MaulingMonkey/jni-bindgen/issues/new) if this is an important
8/// use case for you.
9///
10/// This is a "safe" alternative to jni_sys::JavaVM raw pointers, with the following caveats:
11/// 
12/// 1)  A null vm will result in **undefined behavior**.  Java should not be invoking your native functions with a null
13///     *mut JavaVM, however, so I don't believe this is a problem in practice unless you've bindgened the C header
14///     definitions elsewhere, calling them (requiring `unsafe`), and passing null pointers (generally UB for JNI
15///     functions anyways, so can be seen as a caller soundness issue.)
16/// 
17/// 2)  Allowing the underlying JavaVM to be modified is **undefined behavior**.  I don't believe the JNI libraries
18///     modify the JavaVM, so as long as you're not accepting a *mut JavaVM elsewhere, using unsafe to dereference it,
19///     and mucking with the methods on it yourself, I believe this "should" be fine.
20#[repr(transparent)]
21pub struct VM(JavaVM);
22impl VM {
23    pub fn as_java_vm(&self) -> *const JavaVM { &self.0 }
24    pub unsafe fn from_jni_local(vm: &JavaVM) -> &VM { &*(vm as *const JavaVM as *const VM) }
25
26    pub fn with_env<F, R>(&self, callback: F) -> R
27    where
28        F: FnOnce(&Env) -> R,
29    {
30        let java_vm = self.as_java_vm() as *mut JavaVM;
31        let mut env = null_mut();
32        match unsafe { (**java_vm).GetEnv.unwrap()(java_vm, &mut env, JNI_VERSION_1_2) } {
33            JNI_OK => callback(unsafe { Env::from_jni_void_ref(&env) }),
34            JNI_EDETACHED => match unsafe { (**java_vm).AttachCurrentThread.unwrap()(java_vm, &mut env, null_mut()) } {
35                JNI_OK => callback(unsafe { Env::from_jni_void_ref(&env) }),
36                unexpected => panic!("AttachCurrentThread returned unknown error: {}", unexpected),
37            },
38            JNI_EVERSION => panic!("GetEnv returned JNI_EVERSION"),
39            unexpected => panic!("GetEnv returned unknown error: {}", unexpected),
40        }
41    }
42}
43
44unsafe impl Send for VM {}
45unsafe impl Sync for VM {}
jni_glue/vm.rs

jni_glue/
vm.rs
