Atomic Load/Store

Signed-off-by: Joe Richey <joerichey@google.com>

src/windows.rs

@@ -1,33 +1,47 @@
 //! Implementation for Windows
 use crate::Error;
-use core::mem::MaybeUninit;
-
-extern crate std;
-use std::println;
+use core::{
+    ffi::c_void,
+    mem,
+    mem::MaybeUninit,
+    ptr,
+    sync::atomic::{fence, AtomicPtr, Ordering},
+};
 
 type HMODULE = isize;
 type BOOL = i32;
 const TRUE: BOOL = 1;
 
-type ProcessPrng = unsafe extern "system" fn(*mut u8, usize) -> BOOL;
-
 #[link(name = "kernel32")]
 extern "system" {
     fn LoadLibraryA(libfilename: *const u8) -> HMODULE;
-    fn GetProcAddress(hmodule: HMODULE, procname: *const u8) -> Option<ProcessPrng>;
+    fn GetProcAddress(hmodule: HMODULE, procname: *const u8) -> *mut c_void;
 }
 
-pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    let dll = unsafe { LoadLibraryA(b"bcryptprimitives.dll\0".as_ptr()) };
-    println!("Got DLL: {}", dll);
-    if dll == 0 {
-        return Err(Error::WINDOWS_LOAD_DLL);
+type ProcessPrng = unsafe extern "system" fn(*mut u8, usize) -> BOOL;
+
+static PROCESS_PRNG_PTR: AtomicPtr<c_void> = AtomicPtr::new(ptr::null_mut());
+
+fn get_process_prng() -> Result<ProcessPrng, Error> {
+    let mut p = PROCESS_PRNG_PTR.load(Ordering::Relaxed);
+    if p.is_null() {
+        let dll = unsafe { LoadLibraryA(b"bcryptprimitives.dll\0".as_ptr()) };
+        if dll == 0 {
+            return Err(Error::WINDOWS_LOAD_DLL);
+        }
+        p = unsafe { GetProcAddress(dll, b"ProcessPrng\0".as_ptr()) };
+        if p.is_null() {
+            return Err(Error::WINDOWS_LOAD_DLL);
+        }
+        PROCESS_PRNG_PTR.store(p, Ordering::Release);
+    } else {
+        fence(Ordering::Acquire);
     }
-    let process_prng = match unsafe { GetProcAddress(dll, b"ProcessPrng\0".as_ptr()) } {
-        Some(p) => p,
-        None => return Err(Error::WINDOWS_LOAD_DLL),
-    };
-    println!("Got ProcessPrng: {:p}", process_prng);
+    Ok(unsafe { mem::transmute(p) })
+}
+
+pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
+    let process_prng = get_process_prng()?;
     match unsafe { process_prng(dest.as_mut_ptr() as *mut u8, dest.len()) } {
         TRUE => Ok(()),
         _ => Err(Error::WINDOWS_PROCESS_PRNG),