diff options
| -rw-r--r-- | doc/protocol | 21 | ||||
| -rw-r--r-- | src/bus.c | 11 |
2 files changed, 28 insertions, 4 deletions
diff --git a/doc/protocol b/doc/protocol index def8f6f..a846581 100644 --- a/doc/protocol +++ b/doc/protocol @@ -14,10 +14,14 @@ broadcast: with P(X): Z(W) Write NUL-terminate message to shared memory - with V(N): + with V(N): -- (1) Q := 0 Z(S) + -- (1) may be omitted if semaphores are known that + P(·), Z(·), V(·) cannot create a race condition + with a processes running Z(·). + listen: with V(S): @@ -29,6 +33,17 @@ listen: break with V(W): with P(S): - Z(S) - Z(N) + Z(S) + Z(N) + + +`V(a)` means that semaphore a is released. +`P(a)` means that semaphore a is acquired. +`Z(a)` means that the process waits for semaphore a to become 0. +`with P(a)` that `P(a)` is done before the entering the scope, +and `V(a)` is done when exiting the scope. It also means that +these actions [P(a) and V(a)] are undone when the process exits, +or if the call fails. +`with V(a)` that `V(a)` is like `with P(a)` that `P(a)` and +`V(a)` are exchanged. @@ -623,22 +623,31 @@ fail: int bus_write(const bus_t *bus, const char *message, int flags /* TODO document in man page */) { - int state = 0, saved_errno; + int saved_errno; +#ifndef BUS_SEMAPHORES_ARE_SYNCHRONOUS + int state = 0; +#endif if (acquire_semaphore(bus, X, SEM_UNDO | F(BUS_NOWAIT, IPC_NOWAIT)) == -1) return -1; t(zero_semaphore(bus, W, 0)); write_shared_memory(bus, message); +#ifndef BUS_SEMAPHORES_ARE_SYNCHRONOUS t(release_semaphore(bus, N, SEM_UNDO)); state++; +#endif t(write_semaphore(bus, Q, 0)); t(zero_semaphore(bus, S, 0)); +#ifndef BUS_SEMAPHORES_ARE_SYNCHRONOUS t(acquire_semaphore(bus, N, SEM_UNDO)); state--; +#endif t(release_semaphore(bus, X, SEM_UNDO)); return 0; fail: saved_errno = errno; +#ifndef BUS_SEMAPHORES_ARE_SYNCHRONOUS if (state > 0) acquire_semaphore(bus, N, SEM_UNDO); +#endif release_semaphore(bus, X, SEM_UNDO); errno = saved_errno; return -1; |