Add LazyFd

Author: josephlr

src/lib.rs

@@ -142,11 +142,11 @@ extern crate std;
 
 mod error;
 pub use crate::error::Error;
+
 #[allow(dead_code)]
 mod util;
-
-// These targets need weak linkage to libc randomness functions.
-#[cfg(any(target_os = "macos", target_os = "solaris", target_os = "illumos"))]
+#[cfg(any(unix, target_os = "redox"))]
+#[allow(dead_code)]
 mod util_libc;
 
 // System-specific implementations.

src/util_libc.rs

@@ -36,3 +36,27 @@ impl Weak {
         NonNull::new(addr as *mut _)
     }
 }
+
+pub struct LazyFd(LazyUsize);
+
+impl LazyFd {
+    pub const fn new() -> Self {
+        Self(LazyUsize::new())
+    }
+
+    pub fn init(&self, init: impl FnOnce() -> Option<libc::c_int>) -> Option<libc::c_int> {
+        let fd = self.0.sync_init(
+            || match init() {
+                Some(val) => val as usize,
+                None => LazyUsize::UNINIT,
+            },
+            || unsafe {
+                libc::usleep(1000);
+            },
+        );
+        match fd {
+            LazyUsize::UNINIT => None,
+            val => Some(val as libc::c_int),
+        }
+    }
+}