Function zstd_sys::ZSTDMT_toFlushNow

pub unsafe extern "C" fn ZSTDMT_toFlushNow(
    mtctx: *mut ZSTDMT_CCtx
) -> usize

ZSTDMT_toFlushNow() Tell how many bytes are ready to be flushed immediately. Probe the oldest active job (not yet entirely flushed) and check its output buffer. If return 0, it means there is no active job, or, it means oldest job is still active, but everything produced has been flushed so far, therefore flushing is limited by speed of oldest job.