Fix thread exiting but not being freed

src/libos/src/process/exit.rs

@@ -15,6 +15,7 @@ unsafe impl Send for ChildProcessFilter {}
 pub fn do_exit(exit_status: i32) {
     let current_ref = get_current();
     let mut current = current_ref.lock().unwrap();
+    let parent_ref = current.get_parent().clone();
     // Update current
     current.exit_status = exit_status;
     current.status = Status::ZOMBIE;
@@ -34,8 +35,15 @@ pub fn do_exit(exit_status: i32) {
         futex_wake(ctid as *const i32, 1);
     }
 
+    // If the process is detached, no need to notify the parent
+    if current.is_detached {
+        let current_tid = current.get_tid();
+        drop(current);
+        remove_zombie_child(&parent_ref, current_tid);
+        return;
+    }
+
     // Notify the parent process if necessary
-    let parent_ref = current.get_parent().clone();
     let (mut parent, current) = {
         // Always lock parent before its child
         drop(current);
@@ -103,34 +111,44 @@ pub fn do_wait4(child_filter: &ChildProcessFilter, exit_status: &mut i32) -> Res
         waiter
     };
 
+    // Wait until a child has interesting events
     let child_pid = waiter.sleep_until_woken_with_result();
 
-    let mut current = current_ref.lock().unwrap();
-    let child_i = {
-        let mut child_i_opt = None;
-        for (child_i, child_ref) in current.get_children_iter().enumerate() {
-            let child = child_ref.lock().unwrap();
-            if child.get_pid() != child_pid {
-                continue;
-            }
+    // Remove the child from the parent
+    *exit_status = remove_zombie_child(&current_ref, child_pid);
 
-            if child.get_status() != Status::ZOMBIE {
-                panic!("THIS SHOULD NEVER HAPPEN!");
-            }
-            child_i_opt = Some(child_i);
-            *exit_status = child.get_exit_status();
-        }
-        child_i_opt.unwrap()
-    };
-    current.children.swap_remove(child_i);
+    let mut current = current_ref.lock().unwrap();
     current.waiting_children = None;
 
-    // Release the last reference to the child process
-    process_table::remove(child_pid);
-
     Ok(child_pid)
 }
 
+fn remove_zombie_child(parent_ref: &ProcessRef, child_tid: pid_t) -> i32 {
+    // Find the zombie child process
+    let mut parent = parent_ref.lock().unwrap();
+    let (child_i, child_ref) = parent
+        .get_children_iter()
+        .enumerate()
+        .find(|(child_i, child_ref)| {
+            let child = child_ref.lock().unwrap();
+            if child.get_tid() != child_tid {
+                return false;
+            }
+            assert!(child.get_status() == Status::ZOMBIE);
+            true
+        })
+        .expect("cannot find the zombie child");
+
+    // Remove the zombie child from parent
+    parent.children.swap_remove(child_i);
+    // Remove the zombie child from process table
+    process_table::remove(child_tid);
+
+    // Return the exit status
+    let child = child_ref.lock().unwrap();
+    child.get_exit_status()
+}
+
 fn lock_two_in_order<'a>(
     first_ref: &'a ProcessRef,
     second_ref: &'a ProcessRef,

src/libos/src/process/mod.rs

@@ -23,6 +23,7 @@ pub struct Process {
     tgid: pid_t,
     host_tid: pid_t,
     exit_status: i32,
+    is_detached: bool,
     // TODO: move cwd, root_inode into a FileSystem structure
     // TODO: should cwd be a String or INode?
     cwd: String,

src/libos/src/process/process.rs

@@ -14,6 +14,7 @@ lazy_static! {
             tgid: 0,
             host_tid: 0,
             exit_status: 0,
+            is_detached: false,
             cwd: "/".to_owned(),
             elf_path: "/".to_owned(),
             clear_child_tid: None,
@@ -28,6 +29,7 @@ lazy_static! {
 }
 
 impl Process {
+    // TODO: this constructor has become complicated enough to justify using builders
     pub fn new(
         cwd: &str,
         elf_path: &str,
@@ -35,6 +37,7 @@ impl Process {
         vm_ref: ProcessVMRef,
         file_table_ref: FileTableRef,
         rlimits_ref: ResourceLimitsRef,
+        is_detached: bool,
     ) -> Result<(pid_t, ProcessRef)> {
         let new_pid = process_table::alloc_pid();
         let new_process_ref = Arc::new(SgxMutex::new(Process {
@@ -48,6 +51,7 @@ impl Process {
             elf_path: elf_path.to_owned(),
             clear_child_tid: None,
             exit_status: 0,
+            is_detached: is_detached,
             parent: None,
             children: Vec::new(),
             waiting_children: None,

src/libos/src/process/spawn/mod.rs

@@ -111,7 +111,7 @@ fn new_process(
             Arc::new(SgxMutex::new(files))
         };
         let rlimits_ref = Default::default();
-        Process::new(&cwd, elf_path, task, vm_ref, files_ref, rlimits_ref)?
+        Process::new(&cwd, elf_path, task, vm_ref, files_ref, rlimits_ref, false)?
     };
     parent_adopts_new_child(&parent_ref, &new_process_ref);
     process_table::put(new_pid, new_process_ref.clone());

src/libos/src/process/thread.rs

@@ -79,7 +79,7 @@ pub fn do_clone(
         let rlimits_ref = current.get_rlimits().clone();
         let elf_path = &current.elf_path;
         let cwd = &current.cwd;
-        Process::new(cwd, elf_path, task, vm_ref, files_ref, rlimits_ref)?
+        Process::new(cwd, elf_path, task, vm_ref, files_ref, rlimits_ref, true)?
     };
 
     if let Some(ctid) = ctid {