refault 0.3.0

deterministic simulation framework for distributed systems using async
Documentation 
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use std::sync::LazyLock;

use crate::SimCx;
use rand_core::RngCore;

#[unsafe(no_mangle)]
unsafe extern "C" fn getrandom(buf: *mut u8, buflen: usize, _flags: u32) -> isize {
    SimCx::with(|cx| {
        if let Some(cx3) = cx.once_cell.get() {
            let mut rng = cx3.rng.borrow_mut();
            unsafe {
                // ensure memory is initialized. Hopefully this is optimized out.
                buf.write_bytes(0, buflen);
                rng.fill_bytes(std::slice::from_raw_parts_mut(buf, buflen));
                buflen as isize
            }
        } else {
            // forward to the real getrandom implementation. See man dlsym.
            static GETRANDOM: LazyLock<
                unsafe extern "C" fn(buf: *mut u8, buflen: usize, flags: u32) -> isize,
            > = LazyLock::new(|| unsafe {
                let ptr = libc::dlsym(libc::RTLD_NEXT, c"getrandom".as_ptr() as _);
                assert!(!ptr.is_null());
                std::mem::transmute(ptr)
            });
            unsafe { GETRANDOM(buf, buflen, _flags) }
        }
    })
}

#[unsafe(no_mangle)]
unsafe extern "C" fn clock_gettime(
    _clockid: libc::clockid_t,
    tp: *mut libc::timespec,
) -> libc::c_int {
    SimCx::with(|cx| {
        if let Some(cx3) = cx.once_cell.get() {
            let time = cx3.time.get();
            unsafe {
                tp.write(libc::timespec {
                    tv_sec: time.as_secs() as i64,
                    tv_nsec: time.subsec_nanos() as i64,
                });
                0
            }
        } else {
            // forward to the real clock_gettime implementation. See man dlsym.
            static CLOCK_GETTIME: LazyLock<
                unsafe extern "C" fn(
                    clockid: libc::clockid_t,
                    tp: *mut libc::timespec,
                ) -> libc::c_int,
            > = LazyLock::new(|| unsafe {
                let ptr = libc::dlsym(libc::RTLD_NEXT, c"clock_gettime".as_ptr() as _);
                assert!(!ptr.is_null());
                std::mem::transmute(ptr)
            });
            unsafe { CLOCK_GETTIME(_clockid, tp) }
        }
    })
}