PengZheng commented on code in PR #476:
URL: https://github.com/apache/celix/pull/476#discussion_r1113045950
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documents/framework.md:
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@@ -204,4 +204,75 @@ CELIX_AUTO_START_3=FooBundle.zip
")
add_executable(create_framework_with_celix_launcher src/launcher.c)
target_link_libraries(create_framework_with_celix_launcher PRIVATE
Celix::framework)
-```
\ No newline at end of file
+```
+
+## Framework bundle cache
+The Apache Celix framework uses a bundle cache directory to store the
installed bundles, their state and for a
+persistent bundle storage. The bundle cache directory is created in the
directory configured in the framework
+property `CELIX_FRAMEWORK_CACHE_DIR` (default is ".cache"). A bundle cache
consists of a bundle state property file,
+a resource bundle cache and a persistent storage bundle cache.
+
+The resource bundle cache is used to store and access the bundle resources
(e.g. the content of the bundle zip file)
+and should be treated as read-only. The resource bundle cache can be accessed
using `celix_bundle_getEntry`
+or `celix::Bundle::getEntry`.
+
+The persistent storage bundle cache can be used to store persistent data for a
bundle and can be treated as
+read-write. The persistent storage bundle cache can be accessed using
`celix_bundle_getDataFile` or
+`celix::Bundle::getDataFile`.
+
+If a framework is started with only a `Celix::shell` and `Celix::shell_tui
bundle`, the following directory structure
+is created:
+
+```bash
+% find .cache
+.cache/
+.cache/bundle1
+.cache/bundle1/bundle_state.properties
+.cache/bundle1/storage
+.cache/bundle1/version1.0
+.cache/bundle1/version1.0/libshelld.so.2
+.cache/bundle1/version1.0/libshell.so.2
+.cache/bundle1/version1.0/META-INF
+.cache/bundle1/version1.0/META-INF/MANIFEST.MF
+.cache/bundle2
+.cache/bundle2/bundle_state.properties
+.cache/bundle2/storage
+.cache/bundle2/version1.0
+.cache/bundle2/version1.0/libshell_tuid.so.1
+.cache/bundle2/version1.0/META-INF
+.cache/bundle2/version1.0/META-INF/MANIFEST.MF
+```
+
+The entry `.cache/bundle1/version1.0` is the resource bundle cache and the
entry `.cache/bundle1/storage` is the
+persistent storage bundle cache for the `Celix::shell` bundle.
+
+## Framework configuration options
+The Apache Celix framework can be configured using framework properties.
+
+The framework properties can be provided in the following ways:
+ - Using the Apache Celix launcher with a "config.properties" file.
+ - Creating a framework using the framework factory and providing a
celix_properties_t*.
+ - Setting environment variables with the prefix "CELIX_".
+
+Note that the config properties and environment variables are only read once
when the framework is created.
+So changing the environment variables after the framework is created will not
have any effect.
+
+The following framework properties are supported:
+
+| Framework Property | Default Value |
Description
|
+|-----------------------------------------------------|---------------|-------------------------------------------------------------------------------------------------------------------------------------------|
+| CELIX_FRAMEWORK_CACHE_DIR | ".cache" | The
directory where the Apache Celix framework will store its data.
|
+| CELIX_FRAMEWORK_CACHE_USE_TMP_DIR | "false" | If
true, the Apache Celix framework will use the system temp directory for the
cache directory. |
+| CELIX_FRAMEWORK_CLEAN_CACHE_DIR_ON_CREATE | "false" | If
true, the Apache Celix framework will clean the cache directory on create.
|
+| CELIX_FRAMEWORK_FRAMEWORK_UUID | "" | The
UUID of the Apache Celix framework. If not set, a random UUID will be
generated. |
Review Comment:
IIRC, UUID is always generated in the current implementation.
When Xu, Zhenbao implemented shm-rsa, at first he wanted to rely on UUID to
get a globally unique identity for unix socket. Then he found it impossible,
and used abstract unix socket instead, which is Linux-only.
Another related problem, if I want a stable UUID across restart of the
framework, then I have to store it in persistent storage. What if the storage
component (like config_admin/json_config) is itself a bundle? I guess one
plausible way is to store it in the system bundle's persistent storage cache.
However the current implementation does not support it yet.
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