SerializationSink: Add write_bytes_atomic method.

measureme/src/file_serialization_sink.rs

@@ -1,9 +1,9 @@
 use crate::serialization::{Addr, SerializationSink};
+use parking_lot::Mutex;
 use std::error::Error;
 use std::fs;
-use std::io::{Write};
+use std::io::Write;
 use std::path::Path;
-use parking_lot::Mutex;
 
 pub struct FileSerializationSink {
  data: Mutex<Inner>,
@@ -25,9 +25,9 @@ impl SerializationSink for FileSerializationSink {
  Ok(FileSerializationSink {
  data: Mutex::new(Inner {
  file,
- buffer: vec![0; 1024*512],
+ buffer: vec![0; 1024 * 512],
  buf_pos: 0,
- addr: 0
+ addr: 0,
  }),
  })
  }
@@ -42,7 +42,7 @@ impl SerializationSink for FileSerializationSink {
  ref mut file,
  ref mut buffer,
  ref mut buf_pos,
- ref mut addr
+ ref mut addr,
  } = *data;
 
  let curr_addr = *addr;
@@ -53,15 +53,15 @@ impl SerializationSink for FileSerializationSink {
 
  if buf_end <= buffer.len() {
  // We have enough space in the buffer, just write the data to it.
- write(&mut buffer[buf_start .. buf_end]);
+ write(&mut buffer[buf_start..buf_end]);
  *buf_pos = buf_end;
  } else {
  // We don't have enough space in the buffer, so flush to disk
  file.write_all(&buffer[..buf_start]).unwrap();
 
  if num_bytes <= buffer.len() {
  // There's enough space in the buffer, after flushing
- write(&mut buffer[0 .. num_bytes]);
+ write(&mut buffer[0..num_bytes]);
  *buf_pos = num_bytes;
  } else {
  // Even after flushing the buffer there isn't enough space, so
@@ -75,6 +75,36 @@ impl SerializationSink for FileSerializationSink {
 
  Addr(curr_addr)
  }
+
+ fn write_bytes_atomic(&self, bytes: &[u8]) -> Addr {
+ if bytes.len() < 128 {
+ // For "small" pieces of data, use the regular implementation so we
+ // don't repeatedly flush an almost empty buffer to disk.
+ return self.write_atomic(bytes.len(), |sink| sink.copy_from_slice(bytes));
+ }
+
+ let mut data = self.data.lock();
+ let Inner {
+ ref mut file,
+ ref mut buffer,
+ ref mut buf_pos,
+ ref mut addr,
+ } = *data;
+
+ let curr_addr = *addr;
+ *addr += bytes.len() as u32;
+
+ if *buf_pos > 0 {
+ // There's something in the buffer, flush it to disk
+ file.write_all(&buffer[..*buf_pos]).unwrap();
+ *buf_pos = 0;
+ }
+
+ // Now write the whole input to disk, skipping the write buffer
+ file.write_all(bytes).unwrap();
+
+ Addr(curr_addr)
+ }
 }
 
 impl Drop for FileSerializationSink {

measureme/src/serialization.rs

@@ -1,6 +1,6 @@
+use parking_lot::Mutex;
 use std::error::Error;
 use std::path::Path;
-use parking_lot::Mutex;
 
 #[derive(Clone, Copy, Eq, PartialEq, Debug)]
 pub struct Addr(pub u32);
@@ -14,9 +14,23 @@ impl Addr {
 pub trait SerializationSink: Sized + Send + Sync + 'static {
  fn from_path(path: &Path) -> Result<Self, Box<dyn Error>>;
 
+ /// Atomically write `num_bytes` to the sink. The implementation must ensure
+ /// that concurrent invocations of `write_atomic` do not conflict with each
+ /// other.
+ ///
+ /// The `write` argument is a function that must fill the output buffer
+ /// passed to it. The output buffer is guaranteed to be exactly `num_bytes`
+ /// large.
  fn write_atomic<W>(&self, num_bytes: usize, write: W) -> Addr
  where
  W: FnOnce(&mut [u8]);
+
+ /// Same as write_atomic() but might be faster in cases where bytes to be
+ /// written are already present in a buffer (as opposed to when it is
+ /// benefical to directly serialize into the output buffer).
+ fn write_bytes_atomic(&self, bytes: &[u8]) -> Addr {
+ self.write_atomic(bytes.len(), |sink| sink.copy_from_slice(bytes))
+ }
 }
 
 /// A `SerializationSink` that writes to an internal `Vec<u8>` and can be