[demos] Add a multithread mmap rust demo

demos/rust/.gitignore

@@ -0,0 +1,3 @@
+occlum_instance
+target
+Cargo.lock

demos/rust/README.md

@@ -11,9 +11,9 @@ Refer to tools/toolchains/rust/build.sh for more information.
 
 ## rust\_app
 
-This directory contains source code of a Rust program with a cpp FFI. The cpp
-interface increments the input by one. Rust code calls the function and
-displays the result on the terminal.
+This directory contains source code of a Rust program with two test cases. One is a cpp FFI test, 
+where the cpp interface increments the input by one. The other is a multithreading file backed mmap test. 
+Rust code calls the function and displays the result on the terminal.
 
 One can use occlum-cargo in the way cargo is used. In the rust\_app directory,
 calling ```occlum-cargo build``` will build the demo and ```occlum-cargo run```
@@ -23,5 +23,6 @@ run_rust_demo_on_occlum.sh
 ```
 The output will be displayed on the terminal:
 ```
-5 + 1 = 6
+Cpp FFI test passed!
+Multithreading mmap test passed!
 ```

demos/rust/rust_app/Cargo.toml

@@ -6,6 +6,7 @@ build = "build.rs"
 
 [dependencies]
 libc = "0.2"
+memmap = "0.7.0"
 
 [build-dependencies]
 cc = "1.0"

demos/rust/rust_app/src/main.rs

@@ -1,12 +1,60 @@
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    a::test_cpp_ffi();
+    b::test_multithread_mmap()
+}
+
+mod a {
     extern crate libc;
 
     extern "C" {
         fn increment_by_one(input: *mut libc::c_int);
     }
 
-fn main() {
+    pub fn test_cpp_ffi() {
         let mut input = 5;
         let old = input;
         unsafe { increment_by_one(&mut input) };
-    println!("{} + 1 = {}", old, input);
+        assert_eq!(old + 1, input);
+        println!("Cpp FFI test passed!");
+    }
+}
+
+mod b {
+    use std::fs::File;
+    use std::io::prelude::*;
+    use std::io::{Cursor, Read};
+    use std::thread::{self, JoinHandle};
+
+    pub fn test_multithread_mmap() -> Result<(), Box<dyn std::error::Error>> {
+        let mut file = File::create("/tmp/file.txt")?;
+        writeln!(
+            file,
+            "e785a7d529d589f13e610548b54ac636e30ff4c4e4d834b903b460"
+        )?;
+
+        for _ in 0..1000 {
+            // several thread reads same file
+            let handlers = (1..4)
+                .map(|_| {
+                    thread::spawn(|| -> Result<_, std::io::Error> {
+                        let file = File::open("/tmp/file.txt").unwrap();
+                        let mmap = unsafe { memmap::Mmap::map(&file).unwrap() };
+                        let mut cursor = Cursor::new(mmap.as_ref());
+                        let mut buffer: [u8; 6] = [0; 6];
+                        cursor.read_exact(&mut buffer)?;
+                        Ok(buffer)
+                    })
+                })
+                .collect::<Vec<JoinHandle<Result<_, _>>>>();
+
+            for handler in handlers {
+                match handler.join().unwrap() {
+                    Ok(data) => assert_eq!(b"e785a7", &data),
+                    Err(e) => panic!("Error: {:?}", e),
+                }
+            }
+        }
+        println!("Multithreading mmap test passed!");
+        Ok(())
+    }
 }