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runtime: fix a race condition with async RPCs. 

session.rs has code like:

    while !rpc_queue::empty() {
        try!(process_kern_queued_rpc(stream, &mut session))
    }

    // A

    if mailbox::receive() != 0 {
        try!(process_kern_message(waiter, Some(stream), &mut session));
    }

If both an async and a mailbox RPC (async or large sync) are posted
at point A then they will be processed out of order.
This commit fixes the issue by flushing the async RPC queue before
posting any RPC to the mailbox.
pull/606/head
whitequark 2016-11-01 13:22:22 +00:00
parent 6fcd57a41a
commit b30734a105
1 changed files with 2 additions and 0 deletions
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2
artiq/runtime.rs/libksupport/lib.rs
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@ -107,6 +107,7 @@ extern fn send_rpc(service: u32, tag: *const u8, data: *const *const ()) {
extern { fn strlen(s: *const c_char) -> size_t; }
let tag = unsafe { slice::from_raw_parts(tag, strlen(tag as *const c_char)) };
while !rpc_queue::empty() {}
send(&RpcSend {
async: false,
service: service,
@ -130,6 +131,7 @@ extern fn send_async_rpc(service: u32, tag: *const u8, data: *const *const ()) {
}).unwrap_or_else(|err| {
assert!(err.kind() == std::io::ErrorKind::WriteZero);
while !rpc_queue::empty() {}
send(&RpcSend {
async: true,
service: service,