[Bug 29531] Folder navigation causes audio playback glitches in CDBurnerXP

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=29531

--- Comment #7 from Jörg Höhle <hoehle at users.sourceforge.net> 2012-01-27 10:46:17 CST ---
The sketch of the lock-less design is as follows.
Strive for a particularly simple variant of RCU.  List and partition every
resource that the callback (CB) accesses, i.e. what's shared among CB and API
functions like ReleaseBuffer or Stop.  Make it such that there is one duplex
resource with everything else either Read-Only or Write-Only.

Here's an excerpt of the objects off This->

held_frames     RW => InterlockedAdd

pcm_handle      RO constant
 means valid for the extent of the cb lifetime
fmt->*          RO constant

session->mute is the session pointer constant?

local_buffer    RO constant
bufsize_frames  RO constant
event           RO made constant by upcoming "SetEventHandle once only" patch

started         R variable

lcl_offs_frames WO = CB write pointer

Mmdevapi's "initialize once then never touch" design works towards our goal.

Cannot mix types.  In GetBuffer (API side) or alsa_read_data(CB),
(This->lcl_offs_frames + This->held_frames)
is inacceptable.  Instead, each side must use its own entity.  Split the read
from the write pointer, adding This->xy_offs_frames.  CB updates one, API the
other.

In CB,
+    if(!in_alsa && This->held_frames < This->hidden_frames){
+        UINT32 s_frames = This->hidden_frames - This->held_frames;
can see s_frames < 0.
C in RCU means "Copy" which is trivial here as we use a single RW object. 
Well, RCU is just a guide, what I describe is not RCU.  Our usage of
non-constant objects (held_frames and started) is basic, otherwise we'd need a
"U"(pdate)-like restart transaction loop.

Add extra W variables reflecting error state as needed.  I'm thinking about
using This->initted to hold a steady error state, such as
AUDCLNT_DEVICE_INVALIDATED.

"This->" itself must exist for the life time of CB.  That's why the waitable
event in DeleteTimerQueueTimer is crucial.

Quite straightforward, isn't it?

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