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new 2af0dce Some tweaks to reloading-plugins.en.rst (#6251)
2af0dce is described below
commit 2af0dce59513edaefe4885bc5c77e48666246d08
Author: Brian Neradt <[email protected]>
AuthorDate: Wed Dec 11 14:42:12 2019 -0600
Some tweaks to reloading-plugins.en.rst (#6251)
---
.../design-documents/reloading-plugins.en.rst | 51 +++++++++++-----------
1 file changed, 25 insertions(+), 26 deletions(-)
diff --git a/doc/developer-guide/design-documents/reloading-plugins.en.rst
b/doc/developer-guide/design-documents/reloading-plugins.en.rst
index 23f96e0..7d57341 100644
--- a/doc/developer-guide/design-documents/reloading-plugins.en.rst
+++ b/doc/developer-guide/design-documents/reloading-plugins.en.rst
@@ -22,26 +22,26 @@
Reloading Plugins
*****************
-Reloading plugin allows new versions of a plugin code to be loaded and
executed and old versions to be unloaded without
+The reload plugin mechanism allows new versions of plugin code to be loaded
and executed and old versions to be unloaded without
restarting the |TS| process.
-Plugins are Dynamic Shared Objects (DSO), new versions of the plugins are
currently loaded by using a |TS|
+Plugins are Dynamic Shared Objects (DSO). New versions of the plugins are
currently loaded by using a |TS|
configuration reload, i.e.::
traffic_ctl config reload
-Although this feature should be transparent to there plugin developers, the
following are some design considerations
-and implementation details.
+Although plugin reloading should be transparent to plugin developers, the
following are some design considerations
+and implementation details for this feature.
Design Considerations
=====================
-1. The mechanism of the plugin reload should be transparent to the plugin
developers, plugin developers should be
+1. The mechanism of the plugin reload should be transparent to the plugin
developers. Plugin developers should be
concerned only with properly initializing and cleaning up after the plugin
and its instances.
-2. With the current |TS| implementation new version plugin (re)load is only
triggered by a configuration
- (re)load hence naturally the configuration should be always coupled with
the set of plugins it loaded.
+2. With the current |TS| implementation, new version plugin (re)load is only
triggered by a configuration
+ (re)load. Hence the configuration should always be coupled with the set of
plugins it loaded.
3. Due to its asynchronous nature, |TS| should allow running different newer
and older versions of the same plugin at the same time.
@@ -50,7 +50,7 @@ Design Considerations
5. Running different versions of the configuration and plugin versions at the
same time requires maintaining
a "current active set" to be used by new transactions, new continuations,
etc. and also multiple "previous inactive" sets as well.
-6. The result of the plugin reloading should be consistent across operating
systems, file systems, dynamic loader
+6. The result of the plugin reloading should be consistent across operating
systems, file systems, and dynamic loader
implementations.
@@ -61,10 +61,10 @@ Currently only loading of "remap" plugins (`remap.config`)
is supported but (re)
Consistent (re)loading behavior
-------------------------------
-The following are some of the problems noticed during the initial
experimentation:
+The following are some of the problems noticed during initial experimentation:
a. There is an internal reference counting of the DSOs implemented inside
the dynamic loader.
- If an older version of the plugin DSO is still loaded then loading of a
newer version of the DSO by using
+ If an older version of the plugin DSO is still loaded, then loading of a
newer version of the DSO by using
the same filename does not load the new version.
b. If the filename used by the dynamic loader reference counting contains
symbolic links the results are not
@@ -79,22 +79,22 @@ The following possible solutions were considered:
good results but it was not available on all supported platforms
-A less efficient but more reliable solution was chosen - DSO files are
temporarily copied to and consequently
-loaded from a runtime location and the copies is kept until plugin is unloaded.
+A less efficient but more reliable solution was chosen: DSO files are
temporarily copied to and consequently
+loaded from a runtime location and each copy is kept until the corresponding
plugin is unloaded.
-Each configuration / plugin reload would use a different runtime location,
``ATSUuid`` is used to create unique
+Each configuration / plugin reload would use a different runtime location with
``ATSUuid`` being used to create unique
runtime directories.
Reference counting against DSOs
-------------------------------
-During the initial analysis a common sense solution was considered - to add
instrumentation around handling
+During the initial analysis a common sense solution was considered: add
instrumentation around handling
of registered hooks in order to unload plugins safely. This would be more
involved and not sufficient since hooks
are not the only mechanism that relies on the plugin DSO being loaded. This
design / implementation proposes
a different approach.
-Plugin code can be called from HTTP state machine (1) while handling HTTP
transactions or (2) while calling
+Plugin code can be called from the HTTP state machine (1) while handling HTTP
transactions or (2) while calling
event handling functions of continuations created by the plugin code.
The plugin reload mechanism should guarantee that all necessary plugin DSOs
are still loaded when those calls
are performed.
@@ -103,7 +103,6 @@ Those continuations are created by :c:func:`TSContCreate`
and :c:func:`TSVConnCr
could be used for registering hooks (i.e. registered by
:c:func:`TSHttpHookAdd`) or for
scheduling events in the future (i.e. :c:func:`TSContScheduleOnPool`).
-
Registering hooks always requires creating continuations from inside the
plugin code and a separate
instrumentation around handling of hooks is not necessary.
@@ -117,14 +116,14 @@ Plugin context
--------------
Reference counting and managing different configuration and plugin sets
require the continuation creation and
-destruction to know in which plugin context they are running.
+destruction logic to know in which plugin context they are running.
-Traffic server API change was considered for ``TSCreateCont``,
``TSVConnCreate`` and ``TSDestroyCont`` but
+A |TS| API change was considered for ``TSCreateCont``, ``TSVConnCreate``, and
``TSDestroyCont``, but
it was decided to keep things hidden from the plugin developer by using thread
local plugin context which
would be set/switched accordingly before executing the plugin code.
-The continuations created by the plugin will have a context member added to
them which will be used by
-the reference counting and when continuations are destroyed or handle events.
+The continuations created by the plugin will have a context member added to
them which will be used for
+reference counting, when continuations are destroyed, and to handle events.
TSHttpArgs
@@ -134,7 +133,7 @@ TSHttpArgs
to store information. To avoid collisions between plugins a plugin should
first *reserve* an index in the array.
Since :c:func:`TSHttpTxnArgIndexReserve` and
:c:func:`TSHttpSsnArgIndexReserve` are meant to be called during plugin
-initialization we could end up "leaking" indices during plugins reload.
+initialization we could end up "leaking" indices during plugin reload.
Hence it is necessary to make sure only one index is allocated per "plugin
identifying name", current
:c:func:`TSHttpTxnArgIndexNameLookup` and
:c:func:`TSHttpTxnArgIndexNameLookup` implementation assumes 1-1
index-to-name relationship as well.
@@ -143,12 +142,12 @@ index-to-name relationship as well.
PluginFactory
-------------
-`PluginFactory` - creates and holds all plugin instances corresponding to a
single configuration (re)load.
+`PluginFactory` creates and holds all plugin instances corresponding to a
single configuration (re)load.
-#. Instantiates and initializes 'remap' plugins, eventually signals plugin
unload/destruction, makes sure each plugin
+#. Instantiates and initializes 'remap' plugins, eventually signals plugin
unload/destruction, and makes sure each plugin
version is loaded only once per configuration (re)load by maintaining a
list of DSOs already loaded.
-#. Initializes, keeps track of all resulting plugin instances and eventually
signals each instance destruction.
+#. Initializes and keeps track of all resulting plugin instances and
eventually signals each instance destruction.
#. Handles multiple plugin search paths.
@@ -160,7 +159,7 @@ PluginFactory
RemapPluginInfo
---------------
-`RemapPluginInfo` - a class representing a 'remap' plugin, derived from
`PluginDso`, and handling 'remap' plugin specific
+`RemapPluginInfo` is a class representing a 'remap' plugin. It is derived from
`PluginDso`. It is responsible for handling 'remap' plugin specific
initialization and destruction and also sets up the right plugin context when
its methods are called.
@@ -168,7 +167,7 @@ initialization and destruction and also sets up the right
plugin context when it
PluginDso
---------
-`PluginDso` - a class performing the actual DSO loading and unloading and all
related initialization and
+`PluginDso` is a class performing the actual DSO loading and unloading and all
related initialization and
cleanup plus related error handling. Its functionality is modularized into a
separate class in hopes to
be reused by 'global' plugins in the future.
