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author | anlan_cs <vic.lan@pica8.com> | 2023-06-07 11:29:30 +0200 |
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committer | anlan_cs <vic.lan@pica8.com> | 2023-06-08 09:41:34 +0200 |
commit | 82ff709263be178e52225b84723a5098a32c4f82 (patch) | |
tree | 1b63cc3a17bba423e75795930a2f23e1ebe16dda /doc/developer | |
parent | Merge pull request #13670 from donaldsharp/coverity_99 (diff) | |
download | frr-82ff709263be178e52225b84723a5098a32c4f82.tar.xz frr-82ff709263be178e52225b84723a5098a32c4f82.zip |
doc: Adjust event system
Refer to the latest code, modify the description of event system.
Signed-off-by: anlan_cs <vic.lan@pica8.com>
Diffstat (limited to 'doc/developer')
-rw-r--r-- | doc/developer/process-architecture.rst | 33 |
1 files changed, 17 insertions, 16 deletions
diff --git a/doc/developer/process-architecture.rst b/doc/developer/process-architecture.rst index 33ef278c4..52933a8c1 100644 --- a/doc/developer/process-architecture.rst +++ b/doc/developer/process-architecture.rst @@ -46,7 +46,8 @@ implemented in FRR. This doc should be expanded and broken off into its own section. For now it provides basic information necessary to understand the interplay between the event system and kernel threads. -The core event system is implemented in :file:`lib/thread.[ch]`. The primary +The core event system is implemented in :file:`lib/event.c` and +:file:`lib/frrevent.h`. The primary structure is ``struct event_loop``, hereafter referred to as a ``threadmaster``. A ``threadmaster`` is a global state object, or context, that holds all the tasks currently pending execution as well as statistics on tasks @@ -57,41 +58,41 @@ execute. At initialization, a daemon will typically create one fetch each task and execute it. These tasks have various types corresponding to their general action. The types -are given by integer macros in :file:`event.h` and are: +are given by integer macros in :file:`frrevent.h` and are: -``THREAD_READ`` +``EVENT_READ`` Task which waits for a file descriptor to become ready for reading and then executes. -``THREAD_WRITE`` +``EVENT_WRITE`` Task which waits for a file descriptor to become ready for writing and then executes. -``THREAD_TIMER`` +``EVENT_TIMER`` Task which executes after a certain amount of time has passed since it was scheduled. -``THREAD_EVENT`` +``EVENT_EVENT`` Generic task that executes with high priority and carries an arbitrary integer indicating the event type to its handler. These are commonly used to implement the finite state machines typically found in routing protocols. -``THREAD_READY`` +``EVENT_READY`` Type used internally for tasks on the ready queue. -``THREAD_UNUSED`` +``EVENT_UNUSED`` Type used internally for ``struct event`` objects that aren't being used. The event system pools ``struct event`` to avoid heap allocations; this is the type they have when they're in the pool. -``THREAD_EXECUTE`` +``EVENT_EXECUTE`` Just before a task is run its type is changed to this. This is used to show ``X`` as the type in the output of :clicmd:`show thread cpu`. The programmer never has to work with these types explicitly. Each type of task is created and queued via special-purpose functions (actually macros, but irrelevant for the time being) for the specific type. For example, to add a -``THREAD_READ`` task, you would call +``EVENT_READ`` task, you would call :: @@ -113,9 +114,9 @@ sockets needed for peerings or IPC. To retrieve the next task to run the program calls ``event_fetch()``. ``event_fetch()`` internally computes which task to execute next based on -rudimentary priority logic. Events (type ``THREAD_EVENT``) execute with the +rudimentary priority logic. Events (type ``EVENT_EVENT``) execute with the highest priority, followed by expired timers and finally I/O tasks (type -``THREAD_READ`` and ``THREAD_WRITE``). When scheduling a task a function and an +``EVENT_READ`` and ``EVENT_WRITE``). When scheduling a task a function and an arbitrary argument are provided. The task returned from ``event_fetch()`` is then executed with ``event_call()``. @@ -135,23 +136,23 @@ Mapping the general names used in the figure to specific FRR functions: - ``task`` is ``struct event *`` - ``fetch`` is ``event_fetch()`` -- ``exec()`` is ``event_call`` +- ``exec()`` is ``event_call()`` - ``cancel()`` is ``event_cancel()`` - ``schedule()`` is any of the various task-specific ``event_add_*`` functions Adding tasks is done with various task-specific function-like macros. These -macros wrap underlying functions in :file:`thread.c` to provide additional +macros wrap underlying functions in :file:`event.c` to provide additional information added at compile time, such as the line number the task was scheduled from, that can be accessed at runtime for debugging, logging and informational purposes. Each task type has its own specific scheduling function -that follow the naming convention ``event_add_<type>``; see :file:`event.h` +that follow the naming convention ``event_add_<type>``; see :file:`frrevent.h` for details. There are some gotchas to keep in mind: - I/O tasks are keyed off the file descriptor associated with the I/O operation. This means that for any given file descriptor, only one of each - type of I/O task (``THREAD_READ`` and ``THREAD_WRITE``) can be scheduled. For + type of I/O task (``EVENT_READ`` and ``EVENT_WRITE``) can be scheduled. For example, scheduling two write tasks one after the other will overwrite the first task with the second, resulting in total loss of the first task and difficult bugs. |