Since each Endpoint has a distinct mapping of the packet window, the Go race
detector does not recognize accesses by connected Endpoints to be related. This
means that this change isn't necessary for the Go race detector to accept
accesses of flipcall.Endpoint.Data(), but it *is* necessary for it to accept
accesses to shared variables outside the scope of flipcall that are
synchronized by flipcall.Endpoint state; see updated test for an example.
RaceReleaseMerge is needed (instead of RaceRelease) because calls to
raceBecomeInactive() from *unrelated* Endpoints can occur in any order.
(DowngradableRWMutex.RUnlock() has a similar property: calls to RUnlock() on
the same DowngradableRWMutex from different goroutines can occur in any order.
Remove the TODO asking to explain this now that this is understood.)
PiperOrigin-RevId: 267705325
Note that some of these changes affect the protocol in
backward-incompatible ways.
- Replace use of "initially-active" and "initially-inactive" with
"client" and "server" respectively for clarity.
- Fix a race condition involving Endpoint.Shutdown() by repeatedly
invoking FUTEX_WAKE until it is confirmed that no local thread is
blocked in FUTEX_WAIT.
- Drop flipcall.ControlMode.
PiperOrigin-RevId: 260981382
Flipcall is a (conceptually) simple local-only RPC mechanism. Compared
to unet, Flipcall does not support passing FDs (support for which will
be provided out of band by another package), requires users to establish
connections manually, and requires user management of concurrency since
each connected Endpoint pair supports only a single RPC at a time;
however, it improves performance by using shared memory for data
(reducing memory copies) and using futexes for control signaling (which
is much cheaper than sendto/recvfrom/sendmsg/recvmsg).
PiperOrigin-RevId: 254471986
gVisor bot
Adin Scannell
Jamie Liu
Michael Pratt