take into account the num of processes by ulimit

Author: klim-iv

library/std/src/sys/pal/unix/thread.rs

@@ -440,13 +440,24 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
                     }
                 }
             }
+
+            let mut ulimit = u64::MAX;
+            #[cfg(any(target_os = "android", target_os = "linux"))]
+            {
+                let mut r: libc::rlimit = unsafe { mem::zeroed() };
+                unsafe {
+                    if libc::getrlimit(libc::RLIMIT_NPROC, &mut r) == 0 {
+                        ulimit = r.rlim_max
+                    }
+                }
+            }
             match unsafe { libc::sysconf(libc::_SC_NPROCESSORS_ONLN) } {
                 -1 => Err(io::Error::last_os_error()),
                 0 => Err(io::Error::UNKNOWN_THREAD_COUNT),
                 cpus => {
                     let count = cpus as usize;
                     // Cover the unusual situation where we were able to get the quota but not the affinity mask
-                    let count = count.min(quota);
+                    let count = count.min(quota.min(ulimit.try_into().unwrap_or(usize::MAX)));
                     Ok(unsafe { NonZero::new_unchecked(count) })
                 }
             }