unmapping hopefully..

.gitignore

@@ -1,2 +1,3 @@
 /target
+/test
 *~

src/main.rs

@@ -1,5 +1,6 @@
 #![allow(dead_code)]
 
+use std::convert::TryFrom;
 
 #[macro_export] macro_rules! unwrap {
     (return $($code:expr)?; $err:expr) => {
@@ -38,10 +39,23 @@ fn work(arg::Operation{output, inputs}: arg::Operation) -> Result<(), Box<dyn st
     let output = open::output(output)?;
     //  - open and stat all input files in order (`job::create_from_file`).
     let inputs = open::input(inputs)?;
-    //  - `fallocate` the output file fd to the sum of all input file sizes
+    if inputs.len() == 0 {
+	output.into_inner().set_len(0)?; // Just truncate the output and return
+	return Ok(());
+    }
+    let (jobs, size): (Vec<_>, _) = {
+	let mut off = 0;
+	((0..).zip(inputs.into_iter()).map(|(i, input)| job::create(i, input, &mut off)).collect(), off)
+    };
+    debug_assert!(u64::try_from(size).is_ok(), "Output file too large, would exceed unsigned 64bit integer");
     
+    //  - `fallocate` the output file fd to the sum of all input file sizes
     //  - `mmap` the output file as writable
-    //
+    let output = output.complete(size)?;
+
+    //  - create state
+    let state: state::State = {todo!()};
+    
     //  - spawn the task thread pool
     //  - move the output mapped file to the thread-safe refcounted `state::State`.
     //  - dispatch jobs to the pool with their fds, stats, and calculated output offsets; along with a reference to the output mapped file and a sender for the completion stream (`job::Prelude::start`)
@@ -51,6 +65,12 @@ fn work(arg::Operation{output, inputs}: arg::Operation) -> Result<(), Box<dyn st
     //  - ensure all data was written.
     //  - truncate the output file to the correct size (sum of all the input sizes) if needed (we do not truncate before fallocate()ing it, so if a previous larger file existed there, it will have trailing garbage)
 
+    {
+	use std::io::Write;
+	let mut output = state.try_into_inner().unwrap().unmap();
+	output.set_len(u64::try_from(size).expect("File size is larger than u64::MAX"))?;
+	output.flush()?;
+    }
     Ok(())
 }
 

src/map.rs

@@ -8,8 +8,8 @@ use memmap::MmapMut;
 #[derive(Debug)]
 pub struct MemoryMapMut
 {
-    file: fs::File,
     map: MmapMut,
+    file: fs::File,
 }
 
 impl Drop for MemoryMapMut
@@ -38,6 +38,21 @@ impl AsMut<[u8]> for MemoryMapMut
 
 impl MemoryMapMut
 {
+    /// Unmap this file and return the fd
+    pub fn unmap(self) -> fs::File
+    {
+	use std::{mem, ptr};
+	let mut this = mem::ManuallyDrop::new(self);
+	unsafe {
+	    let map = (&mut this.map as *mut MmapMut).read();
+	    let file = (&mut this.file as *mut fs::File).read();
+	    
+	    let _ = map.flush();
+	    
+	    drop(map);
+	    file
+	}
+    }
     #[inline] pub fn as_slice_mut(&mut self) -> &mut [u8]
     {
 	self.as_mut()

src/open.rs

@@ -27,6 +27,12 @@ pub struct Output(File);
 
 impl Output
 {
+    /// Consume into a normal file.
+    #[inline] pub fn into_inner(self) -> File
+    {
+	self.0
+    }
+    
     /// Allocate this reserved output file `to` bytes, the map it and return.
     pub fn complete(self, to: usize) -> Result<map::MemoryMapMut, OutputError>
     {