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-
-This version of camel is working towards being multi-thread safe
-(MT-SAFE). At least, for the important api's.
-
-This code has now been merged into the main head, but this file
-will remain here as a log of how it was done, incase any issues
-arise. The ChangeLog of course has a much more detailed list
-of changes.
-
-Intended method
-===============
-
-I intend working on it in several stages:
-
-1. Making the api multi-threadable. Basically removing some const-returns,
-and copying some data where it wasn't before. The api should
-still continue to work if not being used in a multithreaded
-application. There is not a significant amount of work here since
-this was more or less the intention all along.
-
-Some functions where references to objects are returned may have to be
-changed slightly, so that refcounts are incremented before return.
-This doesn't affect much though.
-
-camel_folder::get_message_info done
-camel_folder_summary::uid done
-camel_folder_summary::index done
-camel_folder::get_summary
- Needs to ref each summary item it points to. done
-camel_folder::free_summary
- Needs to unref each summary item it points to. done
-camel_folder_get_message_tag
- needs to copy the tag return
-camel_maildir_summary filename string
- should not be able to modify the string
- array contents after it has been added to
- the summary.
-camel_folder done
- Make every camel-folder use a camel-folder-summary.
- This just reduces some of the code duplication,
- since everything but vee-folder does this already.
-
-2. Adding high level locks for proof of concept. The locks will
-be stored in private or global data, so the api should remain the same for
-non-threaded applications.
-
-A per-folder lock which governs access to the folder
- summary, the folder file or
- communications socket, etc. done
-Locking for exceptions. done
-Per store locks for internal stuff. done
-Per-service locks for various internal lists and
- caches done
-
-3. Further fine-grained locking where it can be done/is worthwhile.
-
-A per-index lock for libibex done
-Locking for the search object half done
-Internal lock for the folder_summary itself
- So that searching can be detatched from other
- folder operations, etc. done
-Possibly a lock for access to parts of a mime-part
- or message
-
-4. A method to cancel operations.
-
-Individual outstanding operations must be cancellable, and not just
-'all current operations'. This will probably not use pthread_cancel
-type of cancelling.
-
-This will however, probably use a method for starting a new thread,
-through camel, that can then be cancelled, and/or some method of
-registering that a thread can be cancelled. Blocking states within
-camel, within that thread, will then act as checkpoints for if the
-operation, and if it is cancelled, the operation will abort
-(i.e. fail, with an appropriate exception code).
-
-Operation cancelling should also function when the application is not
-multi-threaded. Not sure of the api for this yet, probably a callback
-system. Hopefully the api for both scenarios can be made the same.
-
-Other thoughts
-==============
-
-Basically much of the code in camel that does the actual work does NOT
-need to be thread safe to make it safely usable in an mt context.
-
-camel-folder, camel-summary, camel-imap-search, and the camel-service
-classes (at least) are the important ones to be made multithreaded.
-
-For other things, they are either resources that are created
-one-off (for example, camel-mime-message, and its associated
-parts, like camel-internet-address), or multithreadedness
-doesn't make a lot of sense - e.g. camel-stream, or camel-mime-parser.
-
-So basically the approach is a low-risk one. Adding the minimum
-number of locks to start with, and providing further fine-grained
-locks as required. The locks should not need to be particularly
-fine-grained in order to get reasonable results.
-
-Log of changes
-==============
-
-Changed CamelFolder:get_message_info() to return a ref'd copy, requiring
-all get_message_info()'s to have a matching free_message_info().
-
-Moved the CamelFolder frozen changelog data to a private structure.
-
-Added a mutex for CamelFolder frozen changelog stuff (it was just easy
-to do, although it isn't needed yet).
-
-Added a single mutex around all other CamelFolder functions that need
-it, this is just the first cut at mt'edness.
-
-Fixed all camel-folder implementations that call any other
-camel-folder functions to call via virtual methods, to bypass the locks.
-
-Added camel-store private data.
-
-Added a single mutex lock for camel-store's folder functions.
-
-Added camel-service private data.
-
-Added a single mutex lock for camel-service's connect stuff.
-
-Added a mutex for remote-store stream io stuff.
-
-Added a mutex for imap, so it can bracket a compound command
-exclusively. Pop doesn't need this since you can only have a single
-folder per store, and the folder interface is already forced
-single-threaded.
-
-Added mutex for camel-session, most operations.
-
-Running the tests finds at least 1 deadlock so far. Need to
-work on that.
-
-Fixed get_summary to ref/unref its items.
-
-Removed the global folder lock from the toplevel
-camel_folder_search(), each implementation must now handle locking.
-
-Fixed the local-folder implementation of searching. imap-folder
-searching should already be mt-safe through the command lock.
-
-Fixed imap summary to ref/unref too.
-
-Built some test cases, and expanded the test framework library to
-handle multiple threads. It works!
-
-Next, added a recursive mutex class, so that locking inside imap had
-any chance of working. Got imap working.
-
-Moved the camel folder summary into the base folder class, and fixed
-everything to use it that way.
-
-Made the vfolder use a real camel-folder-summary rather than a
-hashtable + array that it was using, and probably fixed some problems
-which caused evolution-mail not to always catch flag updates. Oh, and
-made it sync/expunge all its subfolders when sync/expungeing.
-
-Made the camel-folder summary completely mt-safe.
-
-Removed all of the locks on the folder functions dealing directly with
-the summary, so now for example all summary lookups will not be
-interupted by long operations.
-
-Made the nntp newsrc thing mt-safe, because of some unfortunate
-sideeffect of it being called from the summary interaction code in
-nntp-folder.
-