Stream large files during unpacking

Fixes rust-lang#2632, rust-lang#2145, rust-lang#2564

Files over 16M are now written incrementally chunks rather than buffered
in memory in one full linear buffer. This chunk size is not
configurable.

For threaded unpacking, the entire memory buffer will be used to buffer
chunks and a single worker thread will dispatch IO operations from the
buffer, so minimal performance impact should be anticipated (file
size/16M round trips at worst, and most network file systems will
latency hide linear writes).

For immediate unpacking, each chunk is dispatched directly to disk,
which may impact performance as less latency hiding is possible - but
for immediate unpacking clarity of behaviour is the priority.

src/diskio/immediate.rs

@@ -2,27 +2,208 @@
 ///
 /// Use for diagnosing bugs or working around any unexpected issues with the
 /// threaded code paths.
-use super::{perform, Executor, Item};
+use std::{
+    fmt::Debug,
+    fs::{File, OpenOptions},
+    io::{self, Write},
+    path::Path,
+    sync::{Arc, Mutex},
+    time::Instant,
+};
+
+use super::{CompletedIO, Executor, Item};
+
+#[derive(Debug)]
+pub struct _IncrementalFileState {
+    completed_chunks: Vec<usize>,
+    err: Option<io::Result<()>>,
+    item: Option<Item>,
+    finished: bool,
+}
+
+pub(super) type IncrementalFileState = Arc<Mutex<Option<_IncrementalFileState>>>;
+
+#[derive(Default, Debug)]
+pub struct ImmediateUnpacker {
+    incremental_state: IncrementalFileState,
+}
 
-#[derive(Default)]
-pub struct ImmediateUnpacker {}
 impl ImmediateUnpacker {
     pub fn new() -> Self {
-        Self {}
+        Self {
+            ..Default::default()
+        }
+    }
+
+    fn deque(&self) -> Box<dyn Iterator<Item = CompletedIO>> {
+        let mut guard = self.incremental_state.lock().unwrap();
+        // incremental file in progress
+        if let Some(ref mut state) = *guard {
+            // Case 1: pending errors
+            if state.finished {
+                let mut item = state.item.take().unwrap();
+                if state.err.is_some() {
+                    let err = state.err.take().unwrap();
+                    item.result = err;
+                }
+                item.finish = item
+                    .start
+                    .map(|s| Instant::now().saturating_duration_since(s));
+                if state.finished {
+                    *guard = None;
+                }
+                Box::new(Some(CompletedIO::Item(item)).into_iter())
+            } else {
+                // Case 2: pending chunks (which might be empty)
+                let mut completed_chunks = vec![];
+                completed_chunks.append(&mut state.completed_chunks);
+                Box::new(
+                    completed_chunks
+                        .into_iter()
+                        .map(|size| CompletedIO::Chunk(size)),
+                )
+            }
+        } else {
+            Box::new(None.into_iter())
+        }
     }
 }
 
 impl Executor for ImmediateUnpacker {
-    fn dispatch(&self, mut item: Item) -> Box<dyn Iterator<Item = Item> + '_> {
-        perform(&mut item);
-        Box::new(Some(item).into_iter())
+    fn dispatch(&self, mut item: Item) -> Box<dyn Iterator<Item = CompletedIO> + '_> {
+        item.result = match &mut item.kind {
+            super::Kind::Directory => super::create_dir(&item.full_path),
+            super::Kind::File(ref contents) => {
+                super::write_file(&item.full_path, &contents, item.mode)
+            }
+            super::Kind::IncrementalFile(_incremental_file) => {
+                return {
+                    // If there is a pending error, return it, otherwise stash the
+                    // Item for eventual return when the file is finished.
+                    let mut guard = self.incremental_state.lock().unwrap();
+                    if let Some(ref mut state) = *guard {
+                        if state.err.is_some() {
+                            let err = state.err.take().unwrap();
+                            item.result = err;
+                            item.finish = item
+                                .start
+                                .map(|s| Instant::now().saturating_duration_since(s));
+                            *guard = None;
+                            Box::new(Some(CompletedIO::Item(item)).into_iter())
+                        } else {
+                            state.item = Some(item);
+                            Box::new(None.into_iter())
+                        }
+                    } else {
+                        unreachable!();
+                    }
+                };
+            }
+        };
+        item.finish = item
+            .start
+            .map(|s| Instant::now().saturating_duration_since(s));
+        Box::new(Some(CompletedIO::Item(item)).into_iter())
+    }
+
+    fn join(&mut self) -> Box<dyn Iterator<Item = CompletedIO>> {
+        self.deque()
     }
 
-    fn join(&mut self) -> Box<dyn Iterator<Item = Item>> {
-        Box::new(None.into_iter())
+    fn completed(&self) -> Box<dyn Iterator<Item = CompletedIO>> {
+        self.deque()
     }
 
-    fn completed(&self) -> Box<dyn Iterator<Item = Item>> {
-        Box::new(None.into_iter())
+    fn incremental_file_state(&self) -> super::IncrementalFileState {
+        let mut state = self.incremental_state.lock().unwrap();
+        if let Some(_) = *state {
+            unreachable!();
+        } else {
+            *state = Some(_IncrementalFileState {
+                completed_chunks: vec![],
+                err: None,
+                item: None,
+                finished: false,
+            });
+            super::IncrementalFileState::Immediate(self.incremental_state.clone())
+        }
+    }
+}
+
+/// The non-shared state for writing a file incrementally
+#[derive(Debug)]
+pub(super) struct IncrementalFileWriter {
+    state: IncrementalFileState,
+    file: Option<File>,
+    path_display: String,
+}
+
+impl IncrementalFileWriter {
+    #[allow(unused_variables)]
+    pub fn new<P: AsRef<Path>>(
+        path: P,
+        mode: u32,
+        state: IncrementalFileState,
+    ) -> std::result::Result<Self, io::Error> {
+        let mut opts = OpenOptions::new();
+        #[cfg(unix)]
+        {
+            use std::os::unix::fs::OpenOptionsExt;
+            opts.mode(mode);
+        }
+        let path = path.as_ref();
+        let path_display = format!("{}", path.display());
+        let file = Some({
+            trace_scoped!("creat", "name": path_display);
+            opts.write(true).create(true).truncate(true).open(path)?
+        });
+        Ok(IncrementalFileWriter {
+            file,
+            state,
+            path_display,
+        })
+    }
+
+    pub fn chunk_submit(&mut self, chunk: Vec<u8>) -> bool {
+        if (self.state.lock().unwrap()).is_none() {
+            return false;
+        }
+        match self.write(chunk) {
+            Ok(v) => v,
+            Err(e) => {
+                let mut state = self.state.lock().unwrap();
+                if let Some(ref mut state) = *state {
+                    state.err.replace(Err(e));
+                    state.finished = true;
+                    false
+                } else {
+                    false
+                }
+            }
+        }
+    }
+
+    fn write(&mut self, chunk: Vec<u8>) -> std::result::Result<bool, io::Error> {
+        let mut state = self.state.lock().unwrap();
+        if let Some(ref mut state) = *state {
+            if let Some(ref mut file) = (&mut self.file).as_mut() {
+                // Length 0 vector is used for clean EOF signalling.
+                if chunk.len() == 0 {
+                    trace_scoped!("close", "name:": self.path_display);
+                    drop(std::mem::take(&mut self.file));
+                    state.finished = true;
+                } else {
+                    trace_scoped!("write_segment", "name": self.path_display, "len": chunk.len());
+                    file.write_all(&chunk)?;
+
+                    state.completed_chunks.push(chunk.len());
+                }
+                Ok(true)
+            } else {
+                Ok(false)
+            }
+        } else {
+            unreachable!();
+        }
     }
 }