java_spaghetti/
vm.rs

1use std::ptr::null_mut;
2
3use jni_sys::*;
4
5use crate::Env;
6
7/// FFI: Use **&VM** instead of *const JavaVM.  This represents a global, process-wide Java exection environment.
8///
9/// On Android, there is only one VM per-process, although on desktop it's possible (if rare) to have multiple VMs
10/// within the same process.  This library does not support having multiple VMs active simultaniously.
11///
12/// This is a "safe" alternative to jni_sys::JavaVM raw pointers, with the following caveats:
13///
14/// 1)  A null vm will result in **undefined behavior**.  Java should not be invoking your native functions with a null
15///     *mut JavaVM, however, so I don't believe this is a problem in practice unless you've bindgened the C header
16///     definitions elsewhere, calling them (requiring `unsafe`), and passing null pointers (generally UB for JNI
17///     functions anyways, so can be seen as a caller soundness issue.)
18///
19/// 2)  Allowing the underlying JavaVM to be modified is **undefined behavior**.  I don't believe the JNI libraries
20///     modify the JavaVM, so as long as you're not accepting a *mut JavaVM elsewhere, using unsafe to dereference it,
21///     and mucking with the methods on it yourself, I believe this "should" be fine.
22#[repr(transparent)]
23#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
24pub struct VM(*mut JavaVM);
25
26impl VM {
27    pub fn as_raw(&self) -> *mut JavaVM {
28        self.0
29    }
30
31    pub unsafe fn from_raw(vm: *mut JavaVM) -> Self {
32        Self(vm)
33    }
34
35    pub fn with_env<F, R>(&self, callback: F) -> R
36    where
37        F: for<'env> FnOnce(Env<'env>) -> R,
38    {
39        let mut env = null_mut();
40        match unsafe { ((**self.0).v1_2.GetEnv)(self.0, &mut env, JNI_VERSION_1_2) } {
41            JNI_OK => callback(unsafe { Env::from_raw(env as _) }),
42            JNI_EDETACHED => match unsafe { ((**self.0).v1_2.AttachCurrentThread)(self.0, &mut env, null_mut()) } {
43                JNI_OK => callback(unsafe { Env::from_raw(env as _) }),
44                unexpected => panic!("AttachCurrentThread returned unknown error: {}", unexpected),
45            },
46            JNI_EVERSION => panic!("GetEnv returned JNI_EVERSION"),
47            unexpected => panic!("GetEnv returned unknown error: {}", unexpected),
48        }
49    }
50}
51
52unsafe impl Send for VM {}
53unsafe impl Sync for VM {}
java_spaghetti/vm.rs

java_spaghetti/
vm.rs
