add cache for SgxFile

src/libos/src/fs/sgx_impl.rs

@@ -5,11 +5,13 @@ use std::boxed::Box;
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::path::{Path, PathBuf};
 use std::sgxfs::{remove, OpenOptions, SgxFile};
-use std::sync::SgxMutex as Mutex;
+use std::sync::{SgxMutex as Mutex, Arc};
 use std::time::{SystemTime, UNIX_EPOCH};
+use std::collections::BTreeMap;
 
 pub struct SgxStorage {
     path: PathBuf,
+    file_cache: Mutex<BTreeMap<usize, LockedFile>>,
 }
 
 impl SgxStorage {
@@ -17,46 +19,73 @@ impl SgxStorage {
         //        assert!(path.as_ref().is_dir());
         SgxStorage {
             path: path.as_ref().to_path_buf(),
+            file_cache: Mutex::new(BTreeMap::new())
         }
     }
+    /// Get file by `file_id`.
+    /// It lookups cache first, if miss, then call `open_fn` to open one,
+    /// and add it to cache before return.
+    fn get(&self, file_id: usize, open_fn: impl FnOnce(&Self) -> LockedFile) -> LockedFile {
+        // query cache
+        let mut caches = self.file_cache.lock().unwrap();
+        if let Some(locked_file) = caches.get(&file_id) {
+            // hit, return
+            return locked_file.clone();
+        }
+        // miss, open one
+        let locked_file = open_fn(self);
+        // add to cache
+        caches.insert(file_id, locked_file.clone());
+        locked_file
+    }
 }
 
 impl Storage for SgxStorage {
     fn open(&self, file_id: usize) -> DevResult<Box<File>> {
-        let mut path = self.path.to_path_buf();
-        path.push(format!("{}", file_id));
-        // TODO: key
-        let key = [0u8; 16];
-        let file = OpenOptions::new()
-            .read(true)
-            .update(true)
-            .open_ex(path, &key)
-            .expect("failed to open SgxFile");
-        Ok(Box::new(LockedFile(Mutex::new(file))))
+        let locked_file = self.get(file_id, |this| {
+            let mut path = this.path.to_path_buf();
+            path.push(format!("{}", file_id));
+            // TODO: key
+            let key = [0u8; 16];
+            let file = OpenOptions::new()
+                .read(true)
+                .update(true)
+                .open_ex(path, &key)
+                .expect("failed to open SgxFile");
+            LockedFile(Arc::new(Mutex::new(file)))
+        });
+        Ok(Box::new(locked_file))
     }
 
     fn create(&self, file_id: usize) -> DevResult<Box<File>> {
-        let mut path = self.path.to_path_buf();
-        path.push(format!("{}", file_id));
-        // TODO: key
-        let key = [0u8; 16];
-        let file = OpenOptions::new()
-            .write(true)
-            .update(true)
-            .open_ex(path, &key)
-            .expect("failed to create SgxFile");
-        Ok(Box::new(LockedFile(Mutex::new(file))))
+        let locked_file = self.get(file_id, |this| {
+            let mut path = this.path.to_path_buf();
+            path.push(format!("{}", file_id));
+            // TODO: key
+            let key = [0u8; 16];
+            let file = OpenOptions::new()
+                .write(true)
+                .update(true)
+                .open_ex(path, &key)
+                .expect("failed to create SgxFile");
+            LockedFile(Arc::new(Mutex::new(file)))
+        });
+        Ok(Box::new(locked_file))
     }
 
     fn remove(&self, file_id: usize) -> DevResult<()> {
         let mut path = self.path.to_path_buf();
         path.push(format!("{}", file_id));
         remove(path).expect("failed to remove SgxFile");
+        // remove from cache
+        let mut caches = self.file_cache.lock().unwrap();
+        caches.remove(&file_id);
         Ok(())
     }
 }
 
-pub struct LockedFile(Mutex<SgxFile>);
+#[derive(Clone)]
+pub struct LockedFile(Arc<Mutex<SgxFile>>);
 
 // `sgx_tstd::sgxfs::SgxFile` not impl Send ...
 unsafe impl Send for LockedFile {}