allow sharing filesystem between tablebase instances

fuzz/fuzz_targets/pawnful.rs

@@ -3,6 +3,7 @@
 use std::{
     io,
     path::{Path, PathBuf},
+    sync::Arc,
 };
 
 use libfuzzer_sys::fuzz_target;
@@ -56,6 +57,6 @@ fuzz_target!(|data: &[u8]| {
         .into_position(CastlingMode::Standard)
         .expect("valid position");
 
-    let tables = Tablebase::with_filesystem(Box::new(FakeFilesystem { data: data.into() }));
+    let tables = Tablebase::with_filesystem(Arc::new(FakeFilesystem { data: data.into() }));
     let _ = tables.probe_wdl(&pos);
 });

src/filesystem.rs

@@ -6,7 +6,7 @@ use std::{
 };
 
 /// An abstract filesystem.
-pub trait Filesystem: Send + Sync {
+pub trait Filesystem: Sync + Send {
     /// Determines the size in bytes of the given file.
     ///
     /// Follows symbolic links.
@@ -51,7 +51,7 @@ pub enum ReadHint {
 }
 
 /// An abstract randomly readable file.
-pub trait RandomAccessFile: Send + Sync {
+pub trait RandomAccessFile: Sync + Send {
     /// Reads some bytes starting from a given offset.
     ///
     /// See [`std::os::unix::fs::FileExt::read_at()`] for precise semantics.

src/tablebase.rs

@@ -3,6 +3,7 @@ use std::{
     ffi::OsStr,
     fmt, io,
     path::{Path, PathBuf},
+    sync::Arc,
 };
 
 use arrayvec::ArrayVec;
@@ -35,7 +36,7 @@ enum ProbeState {
 
 /// A collection of tables.
 pub struct Tablebase<S: Position + Clone + Syzygy> {
-    filesystem: Box<dyn Filesystem>,
+    filesystem: Arc<dyn Filesystem>,
     wdl: FxHashMap<Material, (PathBuf, OnceCell<WdlTable<S>>)>,
     dtz: FxHashMap<Material, (PathBuf, OnceCell<DtzTable<S>>)>,
     max_pieces: usize,
@@ -63,7 +64,7 @@ impl<S: Position + Clone + Syzygy> Tablebase<S> {
     /// implementation will be used to read table files.
     #[cfg(any(unix, windows))]
     pub fn new() -> Tablebase<S> {
-        Tablebase::with_filesystem(Box::new(filesystem::os::OsFilesystem))
+        Tablebase::with_filesystem(Arc::new(filesystem::os::OsFilesystem))
     }
 
     /// Creates an empty collection of tables. Memory mapping will be used
@@ -85,12 +86,12 @@ impl<S: Position + Clone + Syzygy> Tablebase<S> {
     pub unsafe fn with_mmap_filesystem() -> Tablebase<S> {
         // Safety: Forwarding contract of memmap2::MmapOptions::map()
         // to caller.
-        Tablebase::with_filesystem(unsafe { Box::new(filesystem::mmap::MmapFilesystem::new()) })
+        Tablebase::with_filesystem(unsafe { Arc::new(filesystem::mmap::MmapFilesystem::new()) })
     }
 
     /// Creates an empty collection of tables. A custom filesystem
     /// implementation will be used to read table files.
-    pub fn with_filesystem(filesystem: Box<dyn Filesystem>) -> Tablebase<S> {
+    pub fn with_filesystem(filesystem: Arc<dyn Filesystem>) -> Tablebase<S> {
         Tablebase {
             filesystem,
             wdl: FxHashMap::with_capacity_and_hasher(145, Default::default()),