Check that pthread mutex initialization succeeded

If pthread mutex initialization fails, the failure will go unnoticed unless
debug assertions are enabled. Any subsequent use of mutex will also silently
fail, since return values from lock & unlock operations are similarly checked
only through debug assertions.

In some implementations the mutex initialization requires a memory
allocation and so it does fail in practice.

Check that initialization succeeds to ensure that mutex guarantees
mutual exclusion.

Author: tmiasko

library/std/src/sys/unix/mod.rs

@@ -220,6 +220,10 @@ where
     }
 }
 
+pub fn cvt_nz(error: libc::c_int) -> crate::io::Result<()> {
+    if error == 0 { Ok(()) } else { Err(crate::io::Error::from_raw_os_error(error)) }
+}
+
 // On Unix-like platforms, libc::abort will unregister signal handlers
 // including the SIGABRT handler, preventing the abort from being blocked, and
 // fclose streams, with the side effect of flushing them so libc buffered

library/std/src/sys/unix/mutex.rs

@@ -1,5 +1,6 @@
 use crate::cell::UnsafeCell;
 use crate::mem::MaybeUninit;
+use crate::sys::cvt_nz;
 
 pub struct Mutex {
     inner: UnsafeCell<libc::pthread_mutex_t>,
@@ -51,14 +52,11 @@ impl Mutex {
         // PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
         // re-lock it from the same thread, thus avoiding undefined behavior.
         let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
-        let r = libc::pthread_mutexattr_init(attr.as_mut_ptr());
-        debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutexattr_settype(attr.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL);
-        debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
-        debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
-        debug_assert_eq!(r, 0);
+        cvt_nz(libc::pthread_mutexattr_init(attr.as_mut_ptr())).unwrap();
+        let attr = PthreadMutexAttr(&mut attr);
+        cvt_nz(libc::pthread_mutexattr_settype(attr.0.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL))
+            .unwrap();
+        cvt_nz(libc::pthread_mutex_init(self.inner.get(), attr.0.as_ptr())).unwrap();
     }
     #[inline]
     pub unsafe fn lock(&self) {
@@ -106,15 +104,11 @@ impl ReentrantMutex {
 
     pub unsafe fn init(&self) {
         let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
-        let result = libc::pthread_mutexattr_init(attr.as_mut_ptr());
-        debug_assert_eq!(result, 0);
-        let result =
-            libc::pthread_mutexattr_settype(attr.as_mut_ptr(), libc::PTHREAD_MUTEX_RECURSIVE);
-        debug_assert_eq!(result, 0);
-        let result = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
-        debug_assert_eq!(result, 0);
-        let result = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
-        debug_assert_eq!(result, 0);
+        cvt_nz(libc::pthread_mutexattr_init(attr.as_mut_ptr())).unwrap();
+        let attr = PthreadMutexAttr(&mut attr);
+        cvt_nz(libc::pthread_mutexattr_settype(attr.0.as_mut_ptr(), libc::PTHREAD_MUTEX_RECURSIVE))
+            .unwrap();
+        cvt_nz(libc::pthread_mutex_init(self.inner.get(), attr.0.as_ptr())).unwrap();
     }
 
     pub unsafe fn lock(&self) {
@@ -137,3 +131,14 @@ impl ReentrantMutex {
         debug_assert_eq!(result, 0);
     }
 }
+
+struct PthreadMutexAttr<'a>(&'a mut MaybeUninit<libc::pthread_mutexattr_t>);
+
+impl Drop for PthreadMutexAttr<'_> {
+    fn drop(&mut self) {
+        unsafe {
+            let result = libc::pthread_mutexattr_destroy(self.0.as_mut_ptr());
+            debug_assert_eq!(result, 0);
+        }
+    }
+}

library/std/src/sys/unix/process/process_unix.rs

@@ -281,7 +281,7 @@ impl Command {
         envp: Option<&CStringArray>,
     ) -> io::Result<Option<Process>> {
         use crate::mem::MaybeUninit;
-        use crate::sys;
+        use crate::sys::{self, cvt_nz};
 
         if self.get_gid().is_some()
             || self.get_uid().is_some()
@@ -343,10 +343,6 @@ impl Command {
             }
         }
 
-        fn cvt_nz(error: libc::c_int) -> io::Result<()> {
-            if error == 0 { Ok(()) } else { Err(io::Error::from_raw_os_error(error)) }
-        }
-
         unsafe {
             let mut attrs = MaybeUninit::uninit();
             cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;