Normally we execute the read event first and then the write event.
When the barrier is set, we will do it reverse.
However, under `kqueue`, if an `fd` has both read and write events,
reading the event using `kevent` will generate two events, which will
result in uncontrolled read and write timing.
This also means that the guarantees of AOF `appendfsync` = `always` are
not met on MacOS without this fix.
The main change to this pr is to cache the events already obtained when reading
them, so that if the same `fd` occurs again, only the mask in the cache is updated,
rather than a new event is generated.
This was exposed by the following test failure on MacOS:
```
*** [err]: AOF fsync always barrier issue in tests/integration/aof.tcl
Expected 544 != 544 (context: type eval line 26 cmd {assert {$size1 != $size2}} proc ::test)
```
(cherry picked from commit 306a5ccd2d053ff653988b61a779e3cbce408874)
Sentinel uses execve to run scripts, so it needs to use FD_CLOEXEC
on all file descriptors, so that they're not accessible by the script it runs.
This commit includes a change to the sentinel tests, which verifies no
FDs are left opened when the script is executed.
networking related stuff moved into networking.c
moved more code
more work on layout of source code
SDS instantaneuos memory saving. By Pieter and Salvatore at VMware ;)
cleanly compiling again after the first split, now splitting it in more C files
moving more things around... work in progress
split replication code
splitting more
Sets split
Hash split
replication split
even more splitting
more splitting
minor change
