diff --git a/CMakeLists.txt b/CMakeLists.txt
index ee2befa2d..12cc20e4c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -118,7 +118,7 @@ set(FISH_SRCS
     src/exec.cpp src/expand.cpp src/fallback.cpp src/fish_indent_common.cpp src/fish_version.cpp
     src/flog.cpp src/function.cpp src/highlight.cpp
     src/history.cpp src/history_file.cpp src/input.cpp src/input_common.cpp
-    src/io.cpp src/iothread.cpp src/kill.cpp
+    src/io.cpp src/kill.cpp
     src/null_terminated_array.cpp src/operation_context.cpp src/output.cpp
     src/pager.cpp src/parse_execution.cpp src/parse_util.cpp
     src/parser.cpp src/parser_keywords.cpp src/path.cpp src/postfork.cpp
diff --git a/fish-rust/src/ffi.rs b/fish-rust/src/ffi.rs
index 25f0b3583..afc65e682 100644
--- a/fish-rust/src/ffi.rs
+++ b/fish-rust/src/ffi.rs
@@ -338,3 +338,21 @@ fn from(value: *const autocxx::c_void) -> Self {
         Self(value as *const _)
     }
 }
+
+impl core::convert::From<void_ptr> for *const u8 {
+    fn from(value: void_ptr) -> Self {
+        value.0 as *const _
+    }
+}
+
+impl core::convert::From<void_ptr> for *const core::ffi::c_void {
+    fn from(value: void_ptr) -> Self {
+        value.0 as *const _
+    }
+}
+
+impl core::convert::From<void_ptr> for *const autocxx::c_void {
+    fn from(value: void_ptr) -> Self {
+        value.0 as *const _
+    }
+}
diff --git a/fish-rust/src/threads.rs b/fish-rust/src/threads.rs
index 7fa0fed43..be6f45f31 100644
--- a/fish-rust/src/threads.rs
+++ b/fish-rust/src/threads.rs
@@ -51,6 +51,15 @@ impl FloggableDebug for ThreadId {}
 
 #[cxx::bridge]
 mod ffi {
+    unsafe extern "C++" {
+        include!("callback.h");
+
+        #[rust_name = "CppCallback"]
+        type callback_t;
+        fn invoke(&self) -> *const u8;
+        fn invoke_with_param(&self, param: *const u8) -> *const u8;
+    }
+
     extern "Rust" {
         #[cxx_name = "ASSERT_IS_MAIN_THREAD"]
         fn assert_is_main_thread();
@@ -65,7 +74,7 @@ mod ffi {
 
     extern "Rust" {
         #[cxx_name = "make_detached_pthread"]
-        fn spawn_ffi(callback: *const u8, param: *const u8) -> bool;
+        fn spawn_ffi(callback: &SharedPtr<CppCallback>) -> bool;
     }
 
     extern "Rust" {
@@ -76,9 +85,9 @@ mod ffi {
         #[cxx_name = "iothread_drain_all"]
         fn iothread_drain_all_ffi();
         #[cxx_name = "iothread_perform"]
-        fn iothread_perform_ffi(callback: *const u8, param: *const u8);
+        fn iothread_perform_ffi(callback: &SharedPtr<CppCallback>);
         #[cxx_name = "iothread_perform_cantwait"]
-        fn iothread_perform_cant_wait_ffi(callback: *const u8, param: *const u8);
+        fn iothread_perform_cant_wait_ffi(callback: &SharedPtr<CppCallback>);
     }
 
     extern "Rust" {
@@ -86,14 +95,12 @@ mod ffi {
         type Debounce;
 
         #[cxx_name = "perform"]
-        fn perform_ffi(&self, callback: *const u8, param: *const u8) -> u64;
+        fn perform_ffi(&self, callback: &SharedPtr<CppCallback>) -> u64;
         #[cxx_name = "perform_with_completion"]
         fn perform_with_completion_ffi(
             &self,
-            callback: *const u8,
-            param1: *const u8,
-            completion: *const u8,
-            param2: *const u8,
+            callback: &SharedPtr<CppCallback>,
+            completion: &SharedPtr<CppCallback>,
         ) -> u64;
 
         #[cxx_name = "new_debounce_t"]
@@ -101,6 +108,9 @@ fn perform_with_completion_ffi(
     }
 }
 
+unsafe impl Send for ffi::CppCallback {}
+unsafe impl Sync for ffi::CppCallback {}
+
 fn iothread_service_main_with_timeout_ffi(timeout_usec: u64) {
     iothread_service_main_with_timeout(Duration::from_micros(timeout_usec))
 }
@@ -109,23 +119,19 @@ fn iothread_drain_all_ffi() {
     unsafe { iothread_drain_all() }
 }
 
-fn iothread_perform_ffi(callback: *const u8, param: *const u8) {
-    type Callback = extern "C" fn(crate::ffi::void_ptr);
-    let callback: Callback = unsafe { std::mem::transmute(callback) };
-    let param = param.into();
+fn iothread_perform_ffi(callback: &cxx::SharedPtr<ffi::CppCallback>) {
+    let callback = callback.clone();
 
     iothread_perform(move || {
-        callback(param);
+        callback.invoke();
     });
 }
 
-fn iothread_perform_cant_wait_ffi(callback: *const u8, param: *const u8) {
-    type Callback = extern "C" fn(crate::ffi::void_ptr);
-    let callback: Callback = unsafe { std::mem::transmute(callback) };
-    let param = param.into();
+fn iothread_perform_cant_wait_ffi(callback: &cxx::SharedPtr<ffi::CppCallback>) {
+    let callback = callback.clone();
 
     iothread_perform_cant_wait(move || {
-        callback(param);
+        callback.invoke();
     });
 }
 
@@ -286,13 +292,10 @@ pub fn spawn<F: FnOnce() + Send + 'static>(callback: F) -> bool {
     result
 }
 
-fn spawn_ffi(callback: *const u8, param: *const u8) -> bool {
-    type Callback = extern "C" fn(crate::ffi::void_ptr);
-    let callback: Callback = unsafe { std::mem::transmute(callback) };
-    let param = param.into();
-
+fn spawn_ffi(callback: &cxx::SharedPtr<ffi::CppCallback>) -> bool {
+    let callback = callback.clone();
     spawn(move || {
-        callback(param);
+        callback.invoke();
     })
 }
 
@@ -645,38 +648,29 @@ pub fn perform(&self, handler: impl FnOnce() + 'static + Send) -> NonZeroU64 {
         self.perform_inner(h)
     }
 
-    fn perform_with_completion_ffi(
-        &self,
-        callback: *const u8,
-        param1: *const u8,
-        completion_callback: *const u8,
-        param2: *const u8,
-    ) -> u64 {
-        type Callback = extern "C" fn(crate::ffi::void_ptr) -> crate::ffi::void_ptr;
-        type CompletionCallback = extern "C" fn(crate::ffi::void_ptr, crate::ffi::void_ptr);
+    fn perform_ffi(&self, callback: &cxx::SharedPtr<ffi::CppCallback>) -> u64 {
+        let callback = callback.clone();
 
-        let callback: Callback = unsafe { std::mem::transmute(callback) };
-        let param1 = param1.into();
-        let completion_callback: CompletionCallback =
-            unsafe { std::mem::transmute(completion_callback) };
-        let param2 = param2.into();
-
-        self.perform_with_completion(
-            move || callback(param1),
-            move |result| completion_callback(param2, result),
-        )
+        self.perform(move || {
+            callback.invoke();
+        })
         .into()
     }
 
-    fn perform_ffi(&self, callback: *const u8, param: *const u8) -> u64 {
-        type Callback = extern "C" fn(crate::ffi::void_ptr);
+    fn perform_with_completion_ffi(
+        &self,
+        callback: &cxx::SharedPtr<ffi::CppCallback>,
+        completion: &cxx::SharedPtr<ffi::CppCallback>,
+    ) -> u64 {
+        let callback = callback.clone();
+        let completion = completion.clone();
 
-        let callback: Callback = unsafe { std::mem::transmute(callback) };
-        let param = param.into();
-
-        self.perform(move || {
-            callback(param);
-        })
+        self.perform_with_completion(
+            move || -> crate::ffi::void_ptr { callback.invoke().into() },
+            move |result| {
+                completion.invoke_with_param(result.into());
+            },
+        )
         .into()
     }
 
diff --git a/src/callback.h b/src/callback.h
new file mode 100644
index 000000000..6201bea7b
--- /dev/null
+++ b/src/callback.h
@@ -0,0 +1,49 @@
+#pragma once
+
+#include <cstdlib>
+#include <functional>
+#include <memory>
+#include <utility>
+#include <vector>
+
+/// A RAII callback container that can be used when the rust code needs to (or might need to) free
+/// up the resources allocated for a callback (either the type-erased std::function wrapping the
+/// lambda itself or the parameter to it.)
+struct callback_t {
+    std::function<void *(const void *param)> callback;
+    std::vector<std::function<void()>> cleanups;
+
+    /// The default no-op constructor for the callback_t type.
+    callback_t() {
+        this->callback = [=](const void *) { return (void *)nullptr; };
+    }
+
+    /// Creates a new callback_t instance wrapping the specified type-erased std::function with an
+    /// optional parameter (defaulting to nullptr).
+    callback_t(std::function<void *(const void *param)> &&callback) {
+        this->callback = std::move(callback);
+    }
+
+    /// Executes the wrapped callback with the parameter stored at the time of creation and returns
+    /// the type-erased (void *) result, but cast to a `const uint8_t *` to please cxx::bridge.
+    const uint8_t *invoke() const {
+        const void *result = callback(nullptr);
+        return (const uint8_t *)result;
+    }
+
+    /// Executes the wrapped callback with the provided parameter and returns the type-erased
+    /// (void *) result, but cast to a `const uint8_t *` to please cxx::bridge.
+    const uint8_t *invoke_with_param(const uint8_t *param) const {
+        const void *result = callback((const void *)param);
+        return (const uint8_t *)result;
+    }
+
+    ~callback_t() {
+        if (cleanups.size() > 0) {
+            for (const std::function<void()> &dtor : cleanups) {
+                (dtor)();
+            }
+            cleanups.clear();
+        }
+    }
+};
diff --git a/src/iothread.cpp b/src/iothread.cpp
deleted file mode 100644
index 0d12dd700..000000000
--- a/src/iothread.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-#include "config.h"  // IWYU pragma: keep
-
-#include "iothread.h"
-
-extern "C" const void *iothread_trampoline(const void *c) {
-    iothread_callback_t *callback = (iothread_callback_t *)c;
-    auto *result = (callback->callback)(callback->param);
-    delete callback;
-    return result;
-}
-
-extern "C" const void *iothread_trampoline2(const void *c, const void *p) {
-    iothread_callback_t *callback = (iothread_callback_t *)c;
-    auto *result = (callback->callback)(p);
-    delete callback;
-    return result;
-}
diff --git a/src/iothread.h b/src/iothread.h
index 2755db112..18dd80c4f 100644
--- a/src/iothread.h
+++ b/src/iothread.h
@@ -1,123 +1,84 @@
-// Handles IO that may hang.
-#ifndef FISH_IOTHREAD_H
-#define FISH_IOTHREAD_H
-#if INCLUDE_RUST_HEADERS
+#pragma once
 
-#include <cstdlib>
-#include <functional>
-#include <memory>
-#include <utility>
+#include <cassert>
 
+#include "callback.h"
 #include "threads.rs.h"
 
-struct iothread_callback_t {
-    std::function<void *(const void *param)> callback;
-    void *param;
-
-    ~iothread_callback_t() {
-        if (param) {
-            free(param);
-            param = nullptr;
-        }
-    }
-};
-
-extern "C" const void *iothread_trampoline(const void *callback);
-extern "C" const void *iothread_trampoline2(const void *callback, const void *param);
-
 // iothread_perform invokes a handler on a background thread.
 inline void iothread_perform(std::function<void()> &&func) {
-    auto callback = new iothread_callback_t{std::bind([=] {
-                                                func();
-                                                return nullptr;
-                                            }),
-                                            nullptr};
+    std::shared_ptr<callback_t> callback = std::make_shared<callback_t>([=](const void *) {
+        func();
+        return nullptr;
+    });
 
-    iothread_perform((const uint8_t *)&iothread_trampoline, (const uint8_t *)callback);
+    iothread_perform(callback);
 }
 
 /// Variant of iothread_perform that disrespects the thread limit.
 /// It does its best to spawn a new thread if all other threads are occupied.
 /// This is for cases where deferring a new thread might lead to deadlock.
 inline void iothread_perform_cantwait(std::function<void()> &&func) {
-    auto callback = new iothread_callback_t{std::bind([=] {
-                                                func();
-                                                return nullptr;
-                                            }),
-                                            nullptr};
+    std::shared_ptr<callback_t> callback = std::make_shared<callback_t>([=](const void *) {
+        func();
+        return nullptr;
+    });
 
-    iothread_perform_cantwait((const uint8_t *)&iothread_trampoline, (const uint8_t *)callback);
+    iothread_perform_cantwait(callback);
 }
 
 inline uint64_t debounce_perform(const debounce_t &debouncer, const std::function<void()> &func) {
-    auto callback = new iothread_callback_t{std::bind([=] {
-                                                func();
-                                                return nullptr;
-                                            }),
-                                            nullptr};
+    std::shared_ptr<callback_t> callback = std::make_shared<callback_t>([=](const void *) {
+        func();
+        return nullptr;
+    });
 
-    return debouncer.perform((const uint8_t *)&iothread_trampoline, (const uint8_t *)callback);
+    return debouncer.perform(callback);
 }
 
 template <typename R>
 inline void debounce_perform_with_completion(const debounce_t &debouncer, std::function<R()> &&func,
                                              std::function<void(R)> &&completion) {
-    auto callback1 = new iothread_callback_t{[=](const void *) {
-                                                 auto *result = new R(func());
-                                                 return (void *)result;
-                                             },
-                                             nullptr};
+    std::shared_ptr<callback_t> callback2 = std::make_shared<callback_t>([=](const void *r) {
+        assert(r != nullptr && "callback1 result was null!");
+        const R *result = (const R *)r;
+        completion(*result);
+        return nullptr;
+    });
 
-    auto callback2 = new iothread_callback_t{
-        ([=](const void *r) {
-            const R *result = (const R *)r;
-            completion(*result);
-            delete result;
-            return nullptr;
-        }),
-        nullptr,
-    };
+    std::shared_ptr<callback_t> callback1 = std::make_shared<callback_t>([=](const void *) {
+        const R *result = new R(func());
+        callback2->cleanups.push_back([result]() { delete result; });
+        return (void *)result;
+    });
 
-    debouncer.perform_with_completion(
-        (const uint8_t *)&iothread_trampoline, (const uint8_t *)callback1,
-        (const uint8_t *)&iothread_trampoline2, (const uint8_t *)callback2);
+    debouncer.perform_with_completion(callback1, callback2);
 }
 
 template <typename R>
 inline void debounce_perform_with_completion(const debounce_t &debouncer, std::function<R()> &&func,
                                              std::function<void(const R &)> &&completion) {
-    auto callback1 = new iothread_callback_t{[=](const void *) {
-                                                 auto *result = new R(func());
-                                                 return (void *)result;
-                                             },
-                                             nullptr};
+    std::shared_ptr<callback_t> callback2 = std::make_shared<callback_t>([=](const void *r) {
+        assert(r != nullptr && "callback1 result was null!");
+        const R *result = (const R *)r;
+        completion(*result);
+        return nullptr;
+    });
 
-    auto callback2 = new iothread_callback_t{
-        ([=](const void *r) {
-            const R *result = (const R *)r;
-            completion(*result);
-            delete result;
-            return nullptr;
-        }),
-        nullptr,
-    };
+    std::shared_ptr<callback_t> callback1 = std::make_shared<callback_t>([=](const void *) {
+        const R *result = new R(func());
+        callback2->cleanups.push_back([result]() { delete result; });
+        return (void *)result;
+    });
 
-    debouncer.perform_with_completion(
-        (const uint8_t *)&iothread_trampoline, (const uint8_t *)callback1,
-        (const uint8_t *)&iothread_trampoline2, (const uint8_t *)callback2);
+    debouncer.perform_with_completion(callback1, callback2);
 }
 
 inline bool make_detached_pthread(const std::function<void()> &func) {
-    auto callback = new iothread_callback_t{
-        [=](const void *) {
-            func();
-            return nullptr;
-        },
-        nullptr,
-    };
+    std::shared_ptr<callback_t> callback = std::make_shared<callback_t>([=](const void *) {
+        func();
+        return nullptr;
+    });
 
-    return make_detached_pthread((const uint8_t *)&iothread_trampoline, (const uint8_t *)callback);
+    return make_detached_pthread(callback);
 }
-
-#endif
-#endif