split / cleanup core utils.

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/sys.rs

@@ -0,0 +1,36 @@
+use tracing::debug;
+
+use crate::Result;
+
+/// This is needed for opening lots of file descriptors, which tends to
+/// happen more often when using RocksDB and making lots of federation
+/// connections at startup. The soft limit is usually 1024, and the hard
+/// limit is usually 512000; I've personally seen it hit >2000.
+///
+/// * <https://www.freedesktop.org/software/systemd/man/systemd.exec.html#id-1.12.2.1.17.6>
+/// * <https://github.com/systemd/systemd/commit/0abf94923b4a95a7d89bc526efc84e7ca2b71741>
+#[cfg(unix)]
+pub fn maximize_fd_limit() -> Result<(), nix::errno::Errno> {
+	use nix::sys::resource::{getrlimit, setrlimit, Resource::RLIMIT_NOFILE as NOFILE};
+
+	let (soft_limit, hard_limit) = getrlimit(NOFILE)?;
+	if soft_limit < hard_limit {
+		setrlimit(NOFILE, hard_limit, hard_limit)?;
+		assert_eq!((hard_limit, hard_limit), getrlimit(NOFILE)?, "getrlimit != setrlimit");
+		debug!(to = hard_limit, from = soft_limit, "Raised RLIMIT_NOFILE",);
+	}
+
+	Ok(())
+}
+
+/// Get the number of threads which could execute in parallel based on the
+/// hardware and administrative constraints of this system. This value should be
+/// used to hint the size of thread-pools and divide-and-conquer algorithms.
+///
+/// * <https://doc.rust-lang.org/std/thread/fn.available_parallelism.html>
+#[must_use]
+pub fn available_parallelism() -> usize {
+	std::thread::available_parallelism()
+		.expect("Unable to query for available parallelism.")
+		.get()
+}