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author | brettw@chromium.org <brettw@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2011-04-15 19:07:43 +0000 |
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committer | brettw@chromium.org <brettw@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2011-04-15 19:07:43 +0000 |
commit | 4a180a518d55c74aea5eb0cda0281d60b78e8a8d (patch) | |
tree | d8356c54cfdfcb567443de574298392dc424cbe6 /ipc/ipc_sync_channel.h | |
parent | de17d3d290d9a63bb117f7e3f956dc9ff4ca6785 (diff) | |
download | chromium_src-4a180a518d55c74aea5eb0cda0281d60b78e8a8d.zip chromium_src-4a180a518d55c74aea5eb0cda0281d60b78e8a8d.tar.gz chromium_src-4a180a518d55c74aea5eb0cda0281d60b78e8a8d.tar.bz2 |
Add additional comments to the sync channel.
TEST=none
BUG=none
Review URL: http://codereview.chromium.org/6864018
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@81779 0039d316-1c4b-4281-b951-d872f2087c98
Diffstat (limited to 'ipc/ipc_sync_channel.h')
-rw-r--r-- | ipc/ipc_sync_channel.h | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/ipc/ipc_sync_channel.h b/ipc/ipc_sync_channel.h index e7ff051..549c35d 100644 --- a/ipc/ipc_sync_channel.h +++ b/ipc/ipc_sync_channel.h @@ -28,6 +28,34 @@ class MessageReplyDeserializer; // This is similar to ChannelProxy, with the added feature of supporting sending // synchronous messages. +// +// Overview of how the sync channel works +// -------------------------------------- +// When the sending thread sends a synchronous message, we create a bunch +// of tracking info (created in SendWithTimeout, stored in the PendingSyncMsg +// structure) associated with the message that we identify by the unique +// "MessageId" on the SyncMessage. Among the things we save is the +// "Deserializer" which is provided by the sync message. This object is in +// charge of reading the parameters from the reply message and putting them in +// the output variables provided by its caller. +// +// The info gets stashed in a queue since we could have a nested stack of sync +// messages (each side could send sync messages in response to sync messages, +// so it works like calling a function). The message is sent to the I/O thread +// for dispatch and the original thread blocks waiting for the reply. +// +// SyncContext maintains the queue in a threadsafe way and listens for replies +// on the I/O thread. When a reply comes in that matches one of the messages +// it's looking for (using the unique message ID), it will execute the +// deserializer stashed from before, and unblock the original thread. +// +// +// Significant complexity results from the fact that messages are still coming +// in while the original thread is blocked. Normal async messages are queued +// and dispatched after the blocking call is complete. Sync messages must +// be dispatched in a reentrant manner to avoid deadlock. +// +// // Note that care must be taken that the lifetime of the ipc_thread argument // is more than this object. If the message loop goes away while this object // is running and it's used to send a message, then it will use the invalid |