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chore: Improve JNI safety #600

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merged 1 commit into from
Jun 27, 2024
Merged

chore: Improve JNI safety #600

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28 changes: 20 additions & 8 deletions core/src/jvm_bridge/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@

use crate::errors::CometResult;

use jni::objects::JClass;
use jni::{
errors::Error,
objects::{JMethodID, JObject, JString, JThrowable, JValueGen, JValueOwned},
Expand Down Expand Up @@ -189,6 +190,12 @@ pub use comet_task_memory_manager::*;

/// The JVM classes that are used in the JNI calls.
pub struct JVMClasses<'a> {
/// Cached JClass for "java.lang.Object"
java_lang_object: JClass<'a>,
/// Cached JClass for "java.lang.Class"
java_lang_class: JClass<'a>,
/// Cached JClass for "java.lang.Throwable"
java_lang_throwable: JClass<'a>,
/// Cached method ID for "java.lang.Object#getClass"
pub object_get_class_method: JMethodID,
/// Cached method ID for "java.lang.Class#getName"
Expand Down Expand Up @@ -224,27 +231,32 @@ impl JVMClasses<'_> {
// `JNIEnv` except for creating the global references of the classes.
let env = unsafe { std::mem::transmute::<&mut JNIEnv, &'static mut JNIEnv>(env) };

let clazz = env.find_class("java/lang/Object").unwrap();
let java_lang_object = env.find_class("java/lang/Object").unwrap();
let object_get_class_method = env
.get_method_id(clazz, "getClass", "()Ljava/lang/Class;")
.get_method_id(&java_lang_object, "getClass", "()Ljava/lang/Class;")
.unwrap();

let clazz = env.find_class("java/lang/Class").unwrap();
let java_lang_class = env.find_class("java/lang/Class").unwrap();
let class_get_name_method = env
.get_method_id(clazz, "getName", "()Ljava/lang/String;")
.get_method_id(&java_lang_class, "getName", "()Ljava/lang/String;")
.unwrap();

let clazz = env.find_class("java/lang/Throwable").unwrap();
let java_lang_throwable = env.find_class("java/lang/Throwable").unwrap();
let throwable_get_message_method = env
.get_method_id(clazz, "getMessage", "()Ljava/lang/String;")
.get_method_id(&java_lang_throwable, "getMessage", "()Ljava/lang/String;")
.unwrap();

let clazz = env.find_class("java/lang/Throwable").unwrap();
let throwable_get_cause_method = env
.get_method_id(clazz, "getCause", "()Ljava/lang/Throwable;")
.get_method_id(&java_lang_throwable, "getCause", "()Ljava/lang/Throwable;")
.unwrap();

// SAFETY: According to the documentation for `JMethodID`, it is our
// responsibility to maintain a reference to the `JClass` instances where the
// methods were accessed from to prevent the methods from being garbage-collected
JVMClasses {
java_lang_object,
java_lang_class,
java_lang_throwable,
object_get_class_method,
class_get_name_method,
throwable_get_message_method,
Expand Down
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