select(2) can only handle file descriptors up to 1024, and there are fairly easy to reproduce
cases where the file descriptor used here is larger than that.
RegionInsertDrag or Consolidate Range or any other operation
calling Playlist::add_region() previously triggered RangesMoved()
which resulted in DiskReader::move_processor_automation()
NB. insert + ripple still moves automation correctly.
strictly speaking the include is not needed here since
g_atomic_compat.h includes glib.h. However it is idempotent,
the file does use glib methods, and g_atomic_compat.h may
one day be removed again.
Previously an empty RegionList was used (auto-partition
changes were never collected at rec-stop), furthermore
auto-partitioned regions do not have an old ARDOUR::AutomationList
(fade in/out) property (_have_old is false).
"While 'atomic' has a volatile qualifier, this is a historical
artifact and the pointer passed to it should not be volatile."
Furthermore "It is very important that all accesses to a
particular integer or pointer be performed using only this API"
(from https://developer.gnome.org/glib/2.68/glib-Atomic-Operations.html)
Hence initialization of atomic variables is changed to also use
this API, instead of directly initializing the value.
This also fixes a few cases where atomic variables were
accessed directly.
see also libs/pbd/pbd/g_atomic_compat.h
By supporting FMA extension, the number of instruction needed
for multiply accumulate to mix channels are reduced. Since,
this extension has been around since middle of 2012, more
computers have this instruction set available.
This uses an atomic counter and spins only on the writer side, which
preserves realtime behavior on the reader side. The spinning yields (by
using the same Boost function from Boost spinlocks) to be
scheduler-friendly.
Fixing this bug also lets us be able to confidently drop garbage early
in the writer if appropriate, so do that and avoid keeping dead wood if
possible.
This reverts commit f95439a502:
"add spinlock to RCU manager to protect concurrent reader() and update() calls"
