fix: drop JNI GlobalRef before detaching thread in memory pool errors

native/core/src/execution/memory_pools/fair_pool.rs

@@ -22,7 +22,10 @@ use std::{
 
 use jni::objects::GlobalRef;
 
-use crate::{errors::CometResult, jvm_bridge::JVMClasses};
+use crate::{
+    errors::{CometError, CometResult},
+    jvm_bridge::JVMClasses,
+};
 use datafusion::common::resources_err;
 use datafusion::execution::memory_pool::MemoryConsumer;
 use datafusion::{
@@ -74,6 +77,7 @@ impl CometFairMemoryPool {
             jni_call!(&mut env,
               comet_task_memory_manager(handle).acquire_memory(additional as i64) -> i64)
         }
+        .map_err(CometError::drop_throwable)
     }
 
     fn release(&self, size: usize) -> CometResult<()> {
@@ -82,6 +86,7 @@ impl CometFairMemoryPool {
         unsafe {
             jni_call!(&mut env, comet_task_memory_manager(handle).release_memory(size as i64) -> ())
         }
+        .map_err(CometError::drop_throwable)
     }
 }
 

native/core/src/execution/memory_pools/unified_pool.rs

@@ -23,7 +23,10 @@ use std::{
     },
 };
 
-use crate::{errors::CometResult, jvm_bridge::JVMClasses};
+use crate::{
+    errors::{CometError, CometResult},
+    jvm_bridge::JVMClasses,
+};
 use datafusion::{
     common::{resources_datafusion_err, DataFusionError},
     execution::memory_pool::{MemoryPool, MemoryReservation},
@@ -68,6 +71,7 @@ impl CometUnifiedMemoryPool {
             jni_call!(&mut env,
               comet_task_memory_manager(handle).acquire_memory(additional as i64) -> i64)
         }
+        .map_err(CometError::drop_throwable)
     }
 
     /// Release memory to Spark's off-heap memory pool via JNI
@@ -77,6 +81,7 @@ impl CometUnifiedMemoryPool {
         unsafe {
             jni_call!(&mut env, comet_task_memory_manager(handle).release_memory(size as i64) -> ())
         }
+        .map_err(CometError::drop_throwable)
     }
 }
 

native/jni-bridge/src/errors.rs

@@ -171,6 +171,25 @@ pub enum CometError {
     },
 }
 
+impl CometError {
+    /// Convert a `JavaException` into an `Internal` error, dropping the JNI
+    /// `GlobalRef` while the current thread is still attached to the JVM.
+    ///
+    /// Call this on errors returned from JNI helper methods that may execute on
+    /// threads not permanently attached to the JVM (e.g. tokio worker threads
+    /// used by the memory pool). Without this, the `GlobalRef` can outlive the
+    /// `AttachGuard` and be dropped on a detached thread, which triggers a
+    /// warning and an expensive temporary attach/detach cycle.
+    pub fn drop_throwable(self) -> Self {
+        match self {
+            CometError::JavaException { class, msg, .. } => {
+                CometError::Internal(format!("{class}: {msg}"))
+            }
+            other => other,
+        }
+    }
+}
+
 pub fn init() {
     std::panic::set_hook(Box::new(|panic_info| {
         // Log the panic message and location to stderr so it is visible in CI logs