[Spice-devel] [PATCH spice-server v2] docs: Add some documentation on spice threading model

[Frediano Ziglio]

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
 .gitignore                     |  1 +
 docs/Makefile.am               |  6 ++--
 docs/spice_threading_model.txt | 74 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+), 2 deletions(-)
 create mode 100644 docs/spice_threading_model.txt

Changes since previous version:
- typos and minor updates.

diff --git a/.gitignore b/.gitignore
index 25db761a..bf618932 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,6 +35,7 @@ INSTALL
 docs/manual/manual.chunked/
 docs/manual/manual.html
 docs/spice_style.html
+docs/spice_threading_model.html
 .dirstamp
 .deps
 .libs
diff --git a/docs/Makefile.am b/docs/Makefile.am
index 3dba2c3a..45667a60 100644
--- a/docs/Makefile.am
+++ b/docs/Makefile.am
@@ -4,14 +4,16 @@ ASCIIDOC_FLAGS = -a icons -a toc
 EXTRA_DIST =					\
 	spice_style.html			\
 	spice_style.txt				\
+	spice_threading_model.html		\
+	spice_threading_model.txt		\
 	$(NULL)
 
 if BUILD_MANUAL
 SUBDIRS = manual
 
-all-local: spice_style.html
+all-local: spice_style.html spice_threading_model.html
 
-spice_style.html: spice_style.txt
+%.html: %.txt
 	$(AM_V_GEN) $(ASCIIDOC) -n $(ASCIIDOC_FLAGS) -o $@ $<
 endif
 
diff --git a/docs/spice_threading_model.txt b/docs/spice_threading_model.txt
new file mode 100644
index 00000000..df492216
--- /dev/null
+++ b/docs/spice_threading_model.txt
@@ -0,0 +1,74 @@
+How does SPICE handle threading
+-------------------------------
+
+Lots of code run in a single thread.
+
+Qemu usually calls SPICE from its main thread except on callbacks to code
+already running in different threads.
+
+Channels (RedChannel/RedChannelClient code) run mostly on a single
+thread except RedChannels on creation and destruction which MUST be
+done in the main thread.
+Lots of channels run in the main thread but currently CursorChannel and
+DisplayChannel are run from within a thread created by RedWorker.
+Note that different CursorChannel/DisplayChannel (they differ by id) run in
+separate RedWorker threads (currently a single RedWorker thread runs a pair
+of CursorChannel and DisplayChannel).
+
+RedChannelClient runs in the RedChannel thread. Creation is done in the same
+thread while destruction can happen in different threads.
+
+A RedClient instance groups the various RedChannelClient connected to
+the same remote SPICE client.
+These RedChannelClient instances can run in separate threads:
+MainChannelClient and most of the other RedChannelClient will be
+running in the main thread, while the CursorChannelClient and the
+DisplayChannelClient usually will be running from a different thread.
+
+Another important aspect of dealing with multiple threads are the dispatchers.
+Dispatchers are used to send messages/request from one thread to another.
+The main dispatcher is used to send requests to the main thread.
+The Qxl uses a dispatcher to send requests to the RedWorker which will forward
+to DisplayChannel/CursorChannel.
+
+RedClient may call some RedChannelClient functions using some callbacks
+registered inside ClientCbs. Usually these callbacks are functions that do the
+job directly if the RedChannel is running in the main thread or they use a
+dispatcher to do the job in the right thread. Currently there are 3 callbacks:
+connect, disconnect and migrate. Connect and migrate are asynchronous (the job
+is done while the current thread is doing something else) while disconnect is
+synchronous (the main thread will wait for termination).
+
+Reference counting and ownership
+--------------------------------
+->  pointer
+
+=>  pointer with owning (mostly GObject ref counting)
+
+RedChannelClient::client -> RedClient
+
+RedClient::channels => RedChannelClient
+
+RedClient::mcc -> MainChannelClient
+
+RedChannelClient::channel => RedChannel
+
+RedChannel::clients -> RedChannelClient
+
+The RedClient represents a connection from a remote SPICE client,
+RedClient::channels corresponding to the connections for the individual
+channels. Their lifetime is tied to the TCP connection to this remote client.
+When a disconnection is detected, the corresponding RedChannelClient are
+removed from RedClient::channels and RedChannel::clients (the main owner of
+RedChannelClient is RedClient).
+When MainChannelClient is disconnected, all RedChannelClients connected to the
+same RedClient are automatically disconnected.
+
+Who owns RedClient? RedClient is released when the MainChannelClient attached
+to it is disconnected. In this case a request is scheduled in the main thread
+(even if MainChannelClient runs on the main thread too) and
+red_client_disconnect is called which calls red_client_destroy which uses
+g_object_unref to free the object.
+
+Where is the MainChannelClient freed? On disconnection like other channel
+clients, currently before RedClient which will have a dangling pointer.
-- 
2.13.5