kgiusti commented on a change in pull request #1301:
URL: https://github.com/apache/qpid-dispatch/pull/1301#discussion_r675802653
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File path: src/adaptors/http2/http2_adaptor.c
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@@ -2496,10 +2657,21 @@ static void handle_connection_event(pn_event_t *e,
qd_server_t *qd_server, void
}
case PN_RAW_CONNECTION_WAKE: {
qd_log(log, QD_LOG_TRACE, "[C%"PRIu64"] PN_RAW_CONNECTION_WAKE
Wake-up", conn->conn_id);
+ if (IS_ATOMIC_FLAG_SET(&conn->q2_restart)) {
Review comment:
Precisely - SET and CLEAR operations must return the *previous* value,
so if (CLEAR_ATOMIC_FLAG()) is true you know it went from True->False ...
atomically.
Imagine two threads running this code concurrently, one sees
IS_ATOMIC_FLAG_SET() as true, enters the IF statement, then immediately swaps
out. The second thread also sees IS_ATOMIC_FLAG_SET() as true and also enters
the IF block. With an atomic CLEAR->return old value it is guaranteed that
only one thread will ever see the return value of True and enter the IF.
That said, it won't make a difference since only one thread is running the
event handler so you're pretty much guaranteed that no other thread will be
making the same IS_XXX CLEAR__XX calls concurrently.
But why do two atomic operations (both of which cause a cache flush) when
one call does both?
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