get process_create working and add tests

src/arena.rs

@@ -20,6 +20,7 @@ use std::mem;
 use std::mem::ManuallyDrop;
 use std::net::TcpListener;
 use std::ops::{Deref, DerefMut};
+use std::process::Child;
 use std::ptr;
 use std::ptr::addr_of_mut;
 use std::ptr::NonNull;
@@ -75,7 +76,8 @@ pub enum ArenaHeaderTag {
     HttpResponse = 0b1000010,
     PipeWriter = 0b1000011,
     Dropped = 0b1000100,
-    PipeReader = 0b1000101,
+    PipeReader = 0b1001001,
+    ChildProcess = 0b1001010,
 }
 
 #[bitfield]
@@ -391,6 +393,19 @@ impl ArenaAllocated for HttpResponse {
     }
 }
 
+impl ArenaAllocated for Child {
+    type Payload = ManuallyDrop<Self>;
+    #[inline]
+    fn tag() -> ArenaHeaderTag {
+        ArenaHeaderTag::ChildProcess
+    }
+}
+impl AllocateInArena<Child> for Child {
+    fn arena_allocate(self, arena: &mut Arena) -> TypedArenaPtr<Child> {
+        Child::alloc(arena, ManuallyDrop::new(self))
+    }
+}
+
 #[repr(C)]
 #[derive(Debug)]
 pub struct AllocSlab {
@@ -556,6 +571,9 @@ unsafe fn drop_slab_in_place(value: NonNull<AllocSlab>, tag: ArenaHeaderTag) {
         ArenaHeaderTag::PipeWriter => {
             drop_typed_slab_in_place!(PipeWriter, value);
         }
+        ArenaHeaderTag::ChildProcess => {
+            drop_typed_slab_in_place!(Child, value);
+        }
         ArenaHeaderTag::NullStream => {
             unreachable!("NullStream is never arena allocated!");
         }