Apache Celix Framework

The Apache Celix framework is the core of Apache Celix applications and provides supports for deployments of dynamic, extensible modules known as bundles.

An instance of an Apache Celix framework can be created with the celix framework factory or by configuring Apache Celix containers using the add_celix_container Apache Celix CMake command.

Framework factory

A new instance of an Apache Celix framework can be created using the C/C++ function/method:

• celix_frameworkFactory_createFramework
• celix::createFramework

When an Apache Celix framework is destroyed it will automatically stop and uninstall all running bundles. For C, an Apache Celix framework needs to be destroyed with the call celix_frameworkFactory_destroyFramework and for C++ this happens when the framework goes out of scope.

Example: Creating an Apache Celix Framework in C

//src/main.c
#include <celix_bundle_activator.h>
int main() {
    //create framework properties
    celix_properties_t* properties = properties_create();
    properties_set(properties, "CELIX_LOGGING_DEFAULT_ACTIVE_LOG_LEVEL", "debug");

    //create framework
    celix_framework_t* fw = celix_frameworkFactory_createFramework(properties);

    //get framework bundle context and log hello
    celix_bundle_context_t* fwContext = celix_framework_getFrameworkContext(fw);
    celix_bundleContext_log(fwContext, CELIX_LOG_LEVEL_INFO, "Hello from framework bundle context");

    //destroy framework
    celix_frameworkFactory_destroyFramework(fw);
}

#CMakeLists.txt
find_package(Celix REQUIRED)
add_executable(create_framework_in_c src/main.c)
target_link_libraries(create_framework_in_c PRIVATE Celix::framework)

Example: Creating an Apache Celix Framework in C++

//src/main.cc
#include <celix/FrameworkFactory.h>
int main() {
    //create framework properties
    celix::Properties properties{};
    properties.set("CELIX_LOGGING_DEFAULT_ACTIVE_LOG_LEVEL", "debug");

    //create framework
    std::shared_ptr<celix::Framework> fw = celix::createFramework(properties);

    //get framework bundle context and log hello
    std::shared_ptr<celix::BundleContext> ctx = fw->getFrameworkBundleContext();
    ctx->logInfo("Hello from framework bundle context");
}

#CMakeLists.txt
find_package(Celix REQUIRED)
add_executable(create_framework_in_cxx src/main.cc)
target_link_libraries(create_framework_in_cxx PRIVATE Celix::framework)

Apache Celix launcher

If the Apache Celix framework is the main application, the Apache Celix launcher can be used to create the framework and wait for a framework shutdown.

The Apache Celix launcher also does some additional work:

• Handles command arguments (mainly to print to embedded and runtime framework properties).
• Tries to read a “config.properties” file from the current workdir and combines this with the optional provided embedded properties to the Apache Celix Launcher.
• Configures a framework shutdown for the SIGINT and SIGTERM signal.
• Configures an “ignore” signal handler for the SIGUSR1 and SIGUSR2 signal.
• Calls the curl_global_init to initialize potential use of curl. Note that the curl_global_init is not thread safe or protected by something like pthread_once.
• Destroys the Apache Celix Framework after shutdown.

Example: Creating an Apache Celix Framework with the Apache Celix Launcher

//src/launcher.c
#include <celix_bundle_activator.h>
int main(int argc, char** argv) {
    return celixLauncher_launchAndWaitForShutdown(argc, argv, NULL);
}

#CMakeLists.txt
find_package(Celix REQUIRED)
add_executable(create_framework_with_celix_launcher src/launcher.c)
target_link_libraries(create_framework_with_celix_launcher PRIVATE Celix::framework)

Installing and starting bundles in an Apache Celix framework

Bundles can be installed and started using the Apache Celix framework bundle context or - when using the Apache Celix launcher - with a “config.properties” file.

Bundles are installed using a path to a zip file. If the path is a relative path, the framework will search for the bundle in the directories configured in the framework property CELIX_BUNDLES_PATH. The default value of CELIX_BUNDLES_PATH is “bundles”.

Another option is to use framework properties to configure which bundles to install and start. This can be done by using the CELIX_AUTO_START_0 till CELIX_AUTO_START_6 framework properties. (note that bundles configured in CELIX_AUTO_START_0 are installed and started first). For a more complete overview of possible framework properties see celix_constants.h

If the Apache Celix launcher is used, the framework properties can be provided with a “config.properties” file using the Java Properties File Format.

Framework properties to install and start bundles:

• CELIX_AUTO_START_0
• CELIX_AUTO_START_1
• CELIX_AUTO_START_2
• CELIX_AUTO_START_3
• CELIX_AUTO_START_4
• CELIX_AUTO_START_5
• CELIX_AUTO_START_6

Example: Installing and starting bundles in C

//src/main.c
#include <celix_bundle_activator.h>
int main() {
    //create framework properties
    celix_properties_t* properties = properties_create();
    properties_set(properties, "CELIX_BUNDLES_PATH", "bundles;/opt/alternative/bundles");
    
    //create framework
    celix_framework_t* fw = celix_frameworkFactory_createFramework(NULL);

    //get framework bundle context and install a bundle
    celix_bundle_context_t* fwContext = celix_framework_getFrameworkContext(fw);
    celix_bundleContext_installBundle(fwContext, "FooBundle.zip", true);

    //destroy framework
    celix_frameworkFactory_destroyFramework(fw);
}

Example: Installing and starting bundles in C++

//src/main.cc
#include <celix/FrameworkFactory.h>
int main() {
    //create framework properties
    celix::Properties properties{};
    properties.set("CELIX_BUNDLES_PATH", "bundles;/opt/alternative/bundles");
    
    //create framework
    std::shared_ptr<celix::Framework> fw = celix::createFramework(properties);
    
    //get framework bundle context and install a bundle
    std::shared_ptr<celix::BundleContext> ctx = fw->getFrameworkBundleContext();
    ctx->installBundle("FooBundle.zip");
}

Example: Installing and starting bundles using the Apache Celix Launcher

//src/launcher.c
#include <celix_bundle_activator.h>
int main(int argc, char** argv) {
    return celixLauncher_launchAndWaitForShutdown(argc, argv, NULL);
}

#CMakeLists.txt
find_package(Celix REQUIRED)
file(GENERATE OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/config.properties CONTENT "
CELIX_BUNDLES_PATH=bundles;/opt/alternative/bundles
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)

Framework celix_condition Services

In a dynamic framework such as Apache Celix, it can sometimes be challenging to ascertain when the framework or certain parts of a dynamic service-based application are ready for use. To address this issue, Apache Celix provides services known as celix_condition services.

A celix_condition service is a registered marker interface with a “condition.id” service property. The service’s availability signifies that the condition identified by the “condition.id” has been met.

The celix_condition service is an adaptation of the OSGi 8 Condition Service Specification.

The Apache Celix framework will provide the following celix_condition services for the respective states:

• Celix condition “true”, which is always available.
• Celix condition “framework.ready”. This service will be registered when the framework has successfully and fully started, which includes installing and starting all configured bundles and services, and ensuring the event queue is empty after all configured bundles have been started. Note that the “framework.ready” condition is not part of the OSGi condition specification.
• Celix condition “framework.error”. This service will be registered when the framework has not started successfully. This can occur if any of the configured bundles fail to start or install. Note that the “framework.error” condition is not part of the OSGi condition specification.

Contrary to the OSGi specification, the Apache Celix framework does not provide a public API for adding or removing framework listeners. Instead, framework condition services can be used. This has the advantage of ensuring no framework state changes can be missed, because the state indicating condition services will be available until the framework is stopped.

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:

% 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: