Add parallel execution example

examples/parallel-guest/src/main.rs

@@ -0,0 +1,82 @@
+#[macro_use]
+extern crate lazy_static;
+
+extern "C" {
+    fn get_hashed_password(ptr: u32, len: u32) -> u32;
+    fn print_char(c: u32);
+}
+
+fn print_str(s: &str) {
+    for c in s.chars() {
+        unsafe { print_char(c as u32) };
+    }
+    unsafe { print_char(b'\n' as u32) };
+}
+
+fn load_hashed_password() -> Option<String> {
+    let mut buffer = String::with_capacity(32);
+    for _ in 0..32 {
+        buffer.push(0 as char);
+    }
+    let result =
+        unsafe { get_hashed_password(buffer.as_mut_ptr() as u32, buffer.capacity() as u32) };
+
+    if result == 0 {
+        Some(buffer)
+    } else {
+        None
+    }
+}
+
+lazy_static! {
+    static ref HASHED_PASSWORD: String = load_hashed_password().unwrap();
+}
+
+static PASSWORD_CHARS: &'static [u8] = b"abcdefghijklmnopqrstuvwxyz0123456789";
+
+// for simplicty we define a scheme for mapping numbers onto passwords
+fn num_to_password(mut num: u64) -> String {
+    let mut extra_zero = num == 0;
+    let mut out = String::new();
+    while num > 0 {
+        out.push(PASSWORD_CHARS[num as usize % PASSWORD_CHARS.len()] as char);
+        extra_zero = extra_zero || num == PASSWORD_CHARS.len() as u64;
+        num /= PASSWORD_CHARS.len() as u64;
+    }
+
+    if extra_zero {
+        out.push(PASSWORD_CHARS[0] as char);
+    }
+
+    out
+}
+
+#[repr(C)]
+struct RetStr {
+    ptr: u32,
+    len: u32,
+}
+
+// returns a (pointer, len) to the password or null
+#[no_mangle]
+fn check_password(from: u64, to: u64) -> u64 {
+    for i in from..to {
+        let password = num_to_password(i);
+        let digest = md5::compute(&password);
+
+        let hash_as_str = format!("{:x}", digest);
+        if hash_as_str == *HASHED_PASSWORD {
+            let ret = RetStr {
+                ptr: password.as_ptr() as usize as u32,
+                len: password.len() as u32,
+            };
+            // leak the data so ending the function doesn't corrupt it, if we cared the host could free it after
+            std::mem::forget(password);
+            return unsafe { std::mem::transmute(ret) };
+        }
+    }
+
+    return 0;
+}
+
+fn main() {}