From 37f724c6568b0247abfde3faf080d27767e9c519 Mon Sep 17 00:00:00 2001
From: "Tate, Hongliang Tian" <tatetian@gmail.com>
Date: Fri, 4 Jan 2019 22:29:36 +0800
Subject: [PATCH] Release Process resources via Weak reference

---
 src/libos/src/process/exit.rs      | 38 +++++++++++++++++-------------
 src/libos/src/process/mod.rs       |  6 ++---
 src/libos/src/process/process.rs   |  2 +-
 src/libos/src/process/spawn/mod.rs |  2 +-
 4 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/src/libos/src/process/exit.rs b/src/libos/src/process/exit.rs
index 21ec212e..b79a3f61 100644
--- a/src/libos/src/process/exit.rs
+++ b/src/libos/src/process/exit.rs
@@ -20,7 +20,8 @@ pub fn do_exit(exit_status: i32) {
     current.status = Status::ZOMBIE;
 
     // Update children
-    for child_ref in &current.children {
+    for child_weak in &current.children {
+        let child_ref = child_weak.upgrade().unwrap();
         let mut child = child_ref.lock().unwrap();
         child.parent = Some(IDLE_PROCESS.clone());
     }
@@ -58,12 +59,13 @@ pub fn do_exit(exit_status: i32) {
 pub fn do_wait4(child_filter: &ChildProcessFilter, exit_status: &mut i32)
     -> Result<pid_t, Error>
 {
+    let current_ref = get_current();
     let waiter = {
-        let current_ref = get_current();
         let mut current = current_ref.lock().unwrap();
 
         let mut any_child_to_wait_for = false;
-        for child_ref in current.get_children() {
+        for child_weak in current.get_children() {
+            let child_ref = child_weak.upgrade().unwrap();
             let child = child_ref.lock().unwrap();
 
             let may_wait_for = match child_filter {
@@ -98,23 +100,27 @@ pub fn do_wait4(child_filter: &ChildProcessFilter, exit_status: &mut i32)
     };
 
     let child_pid = Waiter::sleep_until_woken_with_result(waiter);
-    if child_pid == 0 { panic!("THIS SHOULD NEVER HAPPEN!"); }
 
-    {
-        let current_ref = get_current();
-        let mut current = current_ref.lock().unwrap();
-        current.waiting_children = None;
-    }
+    let mut current = current_ref.lock().unwrap();
+    let child_i = {
+        let mut child_i_opt = None;
+        for (child_i, child_weak) in current.children.iter().enumerate() {
+            let child_ref = child_weak.upgrade().unwrap();
+            let child = child_ref.lock().unwrap();
+            if child.get_pid() != child_pid { continue; }
 
-    let child_ref = process_table::get(child_pid).unwrap();
-    let child = {
-        let child = child_ref.lock().unwrap();
-        if child.get_status() != Status::ZOMBIE {
-            panic!("THIS SHOULD NEVER HAPPEN!");
+            if child.get_status() != Status::ZOMBIE {
+                panic!("THIS SHOULD NEVER HAPPEN!");
+            }
+            child_i_opt = Some(child_i);
+            *exit_status = child.get_exit_status();
         }
-        child
+        child_i_opt.unwrap()
     };
-    *exit_status = child.get_exit_status();
+    current.children.swap_remove(child_i);
+    current.waiting_children = None;
+
+    // Release the last reference to the child process
     process_table::remove(child_pid);
 
     Ok(child_pid)
diff --git a/src/libos/src/process/mod.rs b/src/libos/src/process/mod.rs
index d3fa9d5e..bd58d5c2 100644
--- a/src/libos/src/process/mod.rs
+++ b/src/libos/src/process/mod.rs
@@ -20,14 +20,14 @@ pub struct Process {
     exit_status: i32,
     exec_path: String,
     parent: Option<ProcessRef>,
-    children: Vec<ProcessRef>,
+    children: Vec<ProcessWeakRef>,
     waiting_children: Option<WaitQueue<ChildProcessFilter, pid_t>>,
     vm: ProcessVM,
     file_table: FileTable,
 }
 
 pub type ProcessRef = Arc<SgxMutex<Process>>;
-
+pub type ProcessWeakRef = std::sync::Weak<SgxMutex<Process>>;
 
 pub fn do_getpid() -> pid_t {
     let current_ref = get_current();
@@ -58,7 +58,7 @@ mod spawn;
 mod wait;
 mod exit;
 
-use prelude::*;
+use super::{*};
 use vm::{ProcessVM, VMRangeTrait};
 use fs::{FileTable, File, FileRef};
 use self::task::{Task};
diff --git a/src/libos/src/process/process.rs b/src/libos/src/process/process.rs
index 30a39a39..cfd8c293 100644
--- a/src/libos/src/process/process.rs
+++ b/src/libos/src/process/process.rs
@@ -58,7 +58,7 @@ impl Process {
     pub fn get_files(&self) -> &FileTable { &self.file_table }
     pub fn get_files_mut(&mut self) -> &mut FileTable { &mut self.file_table }
     pub fn get_parent(&self) -> &ProcessRef { self.parent.as_ref().unwrap() }
-    pub fn get_children(&self) -> &[ProcessRef] { &self.children }
+    pub fn get_children(&self) -> &[ProcessWeakRef] { &self.children }
 }
 
 impl Drop for Process {
diff --git a/src/libos/src/process/spawn/mod.rs b/src/libos/src/process/spawn/mod.rs
index e0e9ec94..cd52ab79 100644
--- a/src/libos/src/process/spawn/mod.rs
+++ b/src/libos/src/process/spawn/mod.rs
@@ -109,6 +109,6 @@ fn parent_adopts_new_child(parent_ref: &ProcessRef, child_ref: &ProcessRef)
 {
     let mut parent = parent_ref.lock().unwrap();
     let mut child = child_ref.lock().unwrap();
-    parent.children.push(child_ref.clone());
+    parent.children.push(Arc::downgrade(child_ref));
     child.parent = Some(parent_ref.clone());
 }