vm/vmstart/src/compmgr/component_manager_impl.cpp

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
#include <apr_lib.h>
#include <apr_strings.h>

#include "open/compmgr.h"
#include "component_manager_impl.h"
#include "port_atomic.h"

#define LOG_DOMAIN "compmgr"
#include "clog.h"

/*
 * Private variables and functions. See public fuctions
 * at the end of file.
 */

/**
 * Lock which synchronizes all component manager operations.
 *
 * There is only one component manager instance when several
 * virtual machines coexist in a single process. We synchronize these
 * instances by means of a global lock which is never destroyed.
 *
 * Since component manager does not expect many calls, one lock for
 * all operations is ok from performance perspective.
 */
static apr_thread_rwlock_t* global_lock = NULL;

/**
 * A pool <code>global_lock</code> is allocated from.
 */
static apr_pool_t* global_pool = NULL;

/**
 * A global component manager.
 */
static _ComponentManagerImpl* component_manager_impl = NULL;

/**
 * The length of a preallocated buffer for an error message.
 */
#define MAX_ERROR_BUFFER_SIZE 1024

/**
 * Get an instance information structure for a given instance pointer.
 * @param[out] pp_instance_info_next on return, points to a <code>next</code>
 * slot which points to the corresponding instance info. The slot is used
 * when the instance is to be removed from the list.
 * @param[out] p_component_info on return, points to a handle of
 * a component information structure
 * @param instance the instance handle
 * @return APR_SUCCESS if successful, APR_NOTFOUND if the instance was not
 * found, or another non-zero error code
 */
static int
GetInstanceInfoSlot(_InstanceInfo*** pp_instance_info,
                ComponentInfoHandle* p_component_info,
                OpenInstanceHandle instance) {
    _ComponentInfo* component_info = component_manager_impl->components;
    while (component_info) {
        _InstanceInfo** p_instance_info = &component_info->instances;
        _InstanceInfo* instance_info = component_info->instances;
        while (instance_info) {
            if (instance == instance_info->instance) {
                /* found corresponding information structures */
                *p_component_info = component_info;
                *pp_instance_info = p_instance_info;
                return APR_SUCCESS;
            }
            p_instance_info = &instance_info->next;
            instance_info = instance_info->next;
        }
        component_info = component_info->next;
    }
    return APR_NOTFOUND;
}

/**
 * Get a component information structure for a component
 * with a given name.
 * @param[out] p_component_info on return, points to a handle of
 * a component information structure
 * @param name component name
 * @return APR_SUCCESS if successful, APR_NOTFOUND if a component with
 * the given name cannot be found, or another non-zero error code
 */
static int
GetComponentInfo(ComponentInfoHandle* p_component_info,
                 const char* name) {
    ComponentInfoHandle component_info = component_manager_impl->components;
    while (component_info) {
        if (!strcmp(name, component_info->component->GetName())) {
            /* found a component information structure */
            *p_component_info = component_info;
            return APR_SUCCESS;
        }
        component_info = component_info->next;
    }
    return APR_NOTFOUND;
}

static int
GetComponentInfoSlot(_ComponentInfo*** pp_component_info,
                     const char* name) {
    _ComponentInfo** p_component_info =
        &component_manager_impl->components;
    _ComponentInfo* component_info = component_manager_impl->components;
    while (component_info) {
        if (!strcmp(component_info->component->GetName(), name)) {
            *pp_component_info = p_component_info;
            return APR_SUCCESS;
        }
        p_component_info = &(component_info->next);
        component_info = component_info->next;
    }
    return APR_NOTFOUND;
}


/**
 * Checks if DLL is still used by registered components.
 * @param lib DLL handle
 * @return APR_SUCCESS if DLL is used by some registered component,
 * APR_NOTFOUND otherwise
 */
static int
IsDllInUse(const DllHandle lib) {
    ComponentInfoHandle component_info = component_manager_impl->components;
    while (component_info) {
        if (component_info->declaring_library == lib) {
            /* Found a component information structure,
               which refers to the library */
            return APR_SUCCESS;
        }
        component_info = component_info->next;
    }
    return APR_NOTFOUND;
}

#ifndef NDEBUG
/**
 * Instance sanity check.
 */
static int
is_instance_valid(OpenInstanceHandle instance) {
    ComponentInfoHandle component_info;
    _InstanceInfo** p_instance_info;
    VERIFY_SUCCESS(GetInstanceInfoSlot(&p_instance_info, &component_info, instance));
    return apr_isdigit(*(component_info->component->GetVersion()));
}
#endif

#define ASSERT_IS_INSTANCE_VALID(instance) ASSERT(is_instance_valid(instance), \
    ("Instance is not properly initialized, " \
    "the first strucutre element should point to a default interface table"));


/**
 * Allocate an instance info structure and add it
 * to a component manager list.
 */
static int
AddInstance(OpenInstanceHandle instance,
            ComponentInfoHandle component_info,
            apr_pool_t* pool) {
    CTRACE(("Cm.AddInstance()")); 

    _InstanceInfo* instance_info =
        (_InstanceInfo*) apr_palloc(pool, sizeof(_InstanceInfo));

    if (NULL == instance_info) {
        /* Out of memory */
        return APR_ENOMEM;
    }
    instance_info->pool = pool;
    instance_info->instance = instance;
    instance_info->component_info = component_info;

    instance_info->next = component_info->instances;
    ((struct _ComponentInfo*) component_info)->instances = instance_info;

    ASSERT_IS_INSTANCE_VALID(instance);
    return APR_SUCCESS;
}

/**
 * Unregister an instance and return a pointer to a correspondent
 * instance information structure.
 * @param[out] p_instance_info on return, points to <code>InstanceInfoHandle</code>
 * handle which corresponds to the unregisterd instance
 * @param instance a handle of an instance to be deleted
 * @return APR_SUCCESS if successful, or APR_NOTFOUND if the instance
 * cannot be found
 */
static int
RemoveInstanceInfo(InstanceInfoHandle* p_instance_info,
                   OpenInstanceHandle instance) {
    _InstanceInfo** p_instance_info_next;
    ComponentInfoHandle component_info;

    int ret = GetInstanceInfoSlot(&p_instance_info_next, &component_info, instance);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    *p_instance_info = *p_instance_info_next;
    *p_instance_info_next = (*p_instance_info)->next;
    return APR_SUCCESS;
}

/**
 * Deallocates an instance and the correspondent instance
 * information structure.
 */
static int
FreeInstanceInfo(InstanceInfoHandle instance_info) {
    int ret = instance_info->component_info->
        instance_allocator->FreeInstance(instance_info->instance);
    apr_pool_destroy(instance_info->pool);
    return ret;
}

/**
 * Instance deallocation sequence.
 * <ol>
 * <li>Find a corresponding <code>InstanceInfoHandle</code> structure, and a
 * previous structure from the list</li>
 * <li>Remove the structure from the list</li>
 * <li>Get the <code>ComponentInfoHandle</code> strucutre</li>
 * <li>Use <code>instance_allocator</code> to deallocate an instance</li>
 * <li>Deallocate <code>InstanceInfoHandle</code> by freeing a corresponding pool</li>
 * </ol>
 */
static int
RemoveAndFreeInstanceInfo(OpenInstanceHandle instance) {
    InstanceInfoHandle instance_info;
    int ret = RemoveInstanceInfo(&instance_info, instance);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    return FreeInstanceInfo(instance_info);
}

/**
 * Tries to remove and free all component instances.
 * @return APR_SUCCESS if instances are freed successfully, or
 * the first error code.
 */
static int
FreeComponentInstances(ComponentInfoHandle component_info) {
    int ret = APR_SUCCESS;

    _InstanceInfo* instance_info = component_info->instances;
    while (instance_info) {
        _InstanceInfo* instance_info_next = instance_info->next;
        int ret_new = FreeInstanceInfo(instance_info);
        if (APR_SUCCESS == ret) { /* Store the first error code */
            ret = ret_new;
        }
        instance_info = instance_info_next;
    }
    return ret;
}

/**
 * Removes a given library from a component manager library list.
 *
 * @param lib library handle
 * @return APR_SUCCESS if successful, or a non-zero error code
 */
static int
RemoveLib(DllHandle lib) {
    _Dll** p_library_next =
        &(component_manager_impl->libraries);
    _Dll* library = component_manager_impl->libraries;
    while (library) {
        if (library == lib) {
            *p_library_next = lib->next;
            return APR_SUCCESS;
        }
        p_library_next = &(library->next);
        library = library->next;
    }
    return APR_NOTFOUND;
}

/**
 * Removes the library from a component manager library list and
 * unloads it.
 * @param lib library handle
 * @return APR_SUCCESS if successful, or a non-zero error code
 */
static int
UnloadLib(DllHandle lib) {
    int ret = RemoveLib(lib);
    if (APR_SUCCESS != ret) {
        return ret;
    }
    ret = apr_dso_unload(lib->descriptor);
    apr_pool_destroy(lib->pool);
    return ret;
}

static int
ReleaseLib(DllHandle lib) {
    int ret = IsDllInUse(lib);
    if (APR_NOTFOUND == ret) {
        /* DLL is not used anymore, unload it */
        return UnloadLib(lib);
    }
    return ret;
}

static int
FreeComponentInfo(ComponentInfoHandle component_info) {
    int ret = FreeComponentInstances(component_info);
    DllHandle declaring_library = component_info->declaring_library;
    apr_pool_destroy(component_info->pool);
    if (NULL != declaring_library) {
        ReleaseLib(declaring_library);
    }
    return ret;
}

static int
DumpComponent(OpenComponentHandle component) {
    CTRACE(("%s-%s (Vendor: %s)\nDescription:\t\nInterfaces:\t",
        component->GetName(), component->GetVersion(),
        component->GetVendor(), component->GetDescription()));

    const char** p_name = component->ListInterfaceNames();
    /*
     * String array is NULL terminated. We increase a string pointer until
     * it becomes NULL.
     */
    for(; *p_name; p_name++) {
        CTRACE((" %s", *p_name));
    }
    return APR_SUCCESS;
}

/**
 * Decreases a component reference count. If the count becomes zero,
 * unregisters a component and frees all associated instances.
 * @param name a component name to be unregistered
 * @return APR_SUCCESS if successful, or APR_NOTFOUND if the component
 * cannot be found
 */
static int
RemoveAndFreeComponentInfo(const char* component_name) {
    CTRACE(("static RemoveAndFreeComponentInfo()"));

    _ComponentInfo** p_component_info;
    int ret = GetComponentInfoSlot(&p_component_info, component_name);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    _ComponentInfo* component_info = *p_component_info;
    DumpComponent(component_info->component);

    assert(component_info->num_clients > 0);
    CTRACE(("Removing one of %d component subscribers", component_info->num_clients));

    if (--component_info->num_clients > 0) {
        /* there are still clients for this component, stop here */
        return APR_SUCCESS;
    }

    /* since there are no more cllients, remove the component */
    *p_component_info = component_info->next;
    return FreeComponentInfo(component_info);
}

static int
InitializeGlobalLock() {
    CTRACE(("Cm.InitializeGlobalLock()"));
    if (NULL != global_lock) {
        return APR_SUCCESS;
    }

    int ret = apr_initialize();
    if (APR_SUCCESS != ret) {
        return ret;
    }

    apr_pool_t* pool;
    ret = apr_pool_create(&pool, NULL);
    if (APR_SUCCESS != ret) {
        goto pool_error;
    }

    apr_thread_rwlock_t* lock;
    ret = apr_thread_rwlock_create(&lock, pool);
    if (APR_SUCCESS != ret) {
        goto lock_error;
    }

    /* Atomic replacement of a global component manager lock */
    if (NULL == port_atomic_casptr(
        (volatile void **) &global_lock, (void*) lock, NULL)) {
        /* Successfully placed a lock to a static storage */
        global_pool = pool;
        return APR_SUCCESS;
    } else {
        /* The global lock already exists */

        /*
         * FIXME 
         * Currently apr_thread_rwlock_destroy is called automatically
         * from apr_pool_destroy.
         *
         * ret = apr_thread_rwlock_destroy(lock);
         * apr_pool_destroy(pool);
         * return ret;
         */
        goto lock_error;
    }

lock_error:
    apr_pool_destroy(pool); /* Ignore errors */
pool_error:
    apr_terminate();
    return ret;
}

/*
 * The function deallocates a given component manager.
 * The caller should ensure that the component manager is not still used.
 */
static int
Destroy() {
    CTRACE(("Cm.Destroy()"));
    int ret = APR_SUCCESS, ret_new;

    /* Deallocate all components */
    ComponentInfoHandle component_info = component_manager_impl->components;
    while (NULL != component_info) {
        ComponentInfoHandle component_info_next = component_info->next;
        ret_new = FreeComponentInfo(component_info);
        if (APR_SUCCESS == ret) {
            ret = ret_new;
        }
        component_info = component_info_next;
    }

    apr_pool_destroy(component_manager_impl->pool);
    component_manager_impl = NULL;
    return ret;
}

/**
 * Since <code>_Dll</code> is an internal component
 * manager structure we cannot expose this function
 * as a public interface.
 */
static int
AddComponent(OpenComponentInitializer init_func,
             DllHandle lib,
             apr_pool_t* parent_pool) {
    CTRACE(("static AddComponent()"));

    apr_pool_t* pool;
    int ret = apr_pool_create(&pool, parent_pool);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    _ComponentInfo* new_component_info = (_ComponentInfo*)
        apr_pcalloc(pool, sizeof(_ComponentInfo));
    if (NULL == new_component_info) {
        /* out of memory */
        ret = APR_ENOMEM;
        goto error;
    }

    OpenComponentHandle component;
    ret = init_func(&component, &(new_component_info->instance_allocator),
        pool);
    if (APR_SUCCESS != ret) {
        goto error;
    }
    new_component_info->component = component;
    new_component_info->pool = pool;
    new_component_info->declaring_library = lib;

    DumpComponent(component);

    /* check that the component does not exist */
    ComponentInfoHandle component_info;
    ret = GetComponentInfo(&component_info, component->GetName());

    if (APR_SUCCESS == ret) {
        /* the component with the same name is already registered */
        apr_pool_destroy(pool);
        ((struct _ComponentInfo*) component_info)->num_clients++;
    } else if (APR_NOTFOUND == ret) {
        /* add a new component to the global component manager list */
        new_component_info->next = component_manager_impl->components;
        component_manager_impl->components = new_component_info;
        new_component_info->num_clients = 1;
    } else {
        goto error;
    }
    return APR_SUCCESS;

error:
    apr_pool_destroy(pool);
    return ret;
}

static int
GetOpenComponentInitializer(OpenComponentInitializer* p_init_func,
                            DllHandle lib,
                            const char* init_func_name) {
    return apr_dso_sym((apr_dso_handle_sym_t*) p_init_func,
        lib->descriptor, init_func_name);
}

static int
FindLibrary(DllHandle* p_lib, const char* path) {
    DllHandle lib = component_manager_impl->libraries;

    while (lib) {
        if (!strcmp(lib->path, path)) {
            *p_lib = lib;
            return APR_SUCCESS;
        }
        lib = lib->next;
    }
    return APR_NOTFOUND;
}

/**
 * Loads a library if it is not loaded and registers it in
 * a component manager.
 * @param[out] p_lib on return, points to a library handle
 * @param path platform independent library name
 * @return APR_SUCCESS if successful, or a non-zero error code
 */
static int
LoadLib(DllHandle* p_lib, const char* path) {
    CTRACE(("Cm.LoadLibrary(\"%s\")", path));
    int ret = FindLibrary(p_lib, path);
    if (APR_SUCCESS == ret) {
        return APR_SUCCESS;
    }

    ASSERT(APR_NOTFOUND == ret, \
        ("Unexpected return code from FindLibrary()"));

    apr_pool_t* pool;
    ret = apr_pool_create(&pool, component_manager_impl->pool);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    _Dll* lib = (_Dll*) apr_palloc(pool, sizeof(_Dll));
    if (NULL == lib) {
        apr_pool_destroy(pool);
        return APR_ENOMEM;
    }
    lib->pool = pool;

    /* strdup(lib->path, path); */
    apr_size_t len = strlen(path) + 1;
    lib->path = (char*) apr_palloc(pool, len);
    if (lib->path == NULL) {
        apr_pool_destroy(pool);
        return APR_ENOMEM;
    }
    memcpy(lib->path, path, len);

    ret = apr_dso_load(&lib->descriptor, path, pool);
    if (APR_SUCCESS != ret) {
        char buffer[MAX_ERROR_BUFFER_SIZE];
        apr_dso_error(lib->descriptor,
                buffer, MAX_ERROR_BUFFER_SIZE);
        CTRACE(("Error loading %s: %s", path, buffer));
        apr_pool_destroy(pool);
        return ret;
    }

    lib->next = component_manager_impl->libraries;
    component_manager_impl->libraries = lib;
    *p_lib = lib;
    return APR_SUCCESS;
}

/*
 * The following functions can be accessed
 * by means of a component manager virtual table.
 */
static int
GetComponent(OpenComponentHandle* p_component,
             const char* name) {
    VERIFY_SUCCESS(apr_thread_rwlock_rdlock(global_lock));

    ComponentInfoHandle component_info;
    int ret = GetComponentInfo(&component_info, name);
    if (APR_SUCCESS == ret) {
        *p_component = component_info->component;
    }

    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

static int
GetComponentByInstance(OpenComponentHandle* p_component,
                       OpenInstanceHandle instance) {
    VERIFY_SUCCESS(apr_thread_rwlock_rdlock(global_lock));

    ComponentInfoHandle component_info;
    _InstanceInfo** p_instance_info;

    int ret = GetInstanceInfoSlot(&p_instance_info, &component_info, instance);
    if (APR_SUCCESS == ret) {
        *p_component = component_info->component;
    }

    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

static int
CreateInstance(OpenInstanceHandle* p_instance,
                    const char* name) {
    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));

    ComponentInfoHandle component_info;
    int ret = GetComponentInfo(&component_info, name);
    if (APR_SUCCESS != ret) {
        goto unlock;
    }

    apr_pool_t* pool;
    ret = apr_pool_create(&pool, component_info->pool);
    if (APR_SUCCESS != ret)  {
        goto unlock;
    }

    ret = component_info->instance_allocator->CreateInstance(p_instance, pool);
    if (APR_SUCCESS != ret)  {
        apr_pool_destroy(pool);
        goto unlock;
    }

    ret = AddInstance(*p_instance, component_info, pool);
    if (APR_SUCCESS != ret)  {
         /* ignore errors */
        component_info->instance_allocator->FreeInstance(*p_instance);
        apr_pool_destroy(pool);
    }

unlock:
    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}


static int
FreeInstance(OpenInstanceHandle instance) {
    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));

    int ret = RemoveAndFreeInstanceInfo(instance);

    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

static int
GetInstances(OpenInstanceHandle* p_instance, int buf_len, int* len,
             const char* name) {
    VERIFY_SUCCESS(apr_thread_rwlock_rdlock(global_lock));

    ComponentInfoHandle component_info;
    int ret = GetComponentInfo(&component_info, name);

    if (APR_SUCCESS == ret) {
        *len = 0;
        const OpenInstanceHandle* p_buf_end = p_instance + buf_len;
        _InstanceInfo* instance_info = component_info->instances;

        while (instance_info && p_instance < p_buf_end) {
            *p_instance = instance_info->instance;
            p_instance++;
            (*len)++;
            instance_info = instance_info->next;
        }

        while (instance_info) {
            (*len)++;
            instance_info = instance_info->next;
        }
    }

    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

/**
 * Allocates and fills component manager virtual table.
 */
static int
Create() {
    CTRACE(("Cm.Create()"));

    apr_pool_t* pool;
    int ret = apr_pool_create(&pool, global_pool);
    if (APR_SUCCESS != ret) {
        return ret;
    }

    assert(NULL == component_manager_impl);
    component_manager_impl = (_ComponentManagerImpl*)
        apr_pcalloc(pool, sizeof(_ComponentManagerImpl));
    if (NULL == component_manager_impl) {
        /* Out of memory */
        return APR_ENOMEM;
    }

    component_manager_impl->num_clients = 1;
    component_manager_impl->cm.GetComponent = GetComponent;
    component_manager_impl->cm.GetComponentByInstance = GetComponentByInstance;
    component_manager_impl->cm.CreateInstance = CreateInstance;
    component_manager_impl->cm.FreeInstance = FreeInstance;
    component_manager_impl->cm.GetInstances = GetInstances;
    component_manager_impl->pool = pool;

    return APR_SUCCESS;
}


/*
 * Implementation of public functions.
 */
int
CmAcquire(OpenComponentManagerHandle* p_cm) {
    CTRACE(("Cm.Acquire()"));
    InitializeGlobalLock();

    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));
    if (NULL == component_manager_impl) {
        int ret = Create();
        if (APR_SUCCESS != ret) {
            VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
            return ret;
        }
    } else {
        component_manager_impl->num_clients++;
    }
    CTRACE(("Cm.Acquire(): component_manager_impl->num_clients = %d", component_manager_impl->num_clients));
    *p_cm = (OpenComponentManagerHandle) component_manager_impl;
    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return APR_SUCCESS;
}

int
CmRelease() {
    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));
    component_manager_impl->num_clients--;

    int ret = APR_SUCCESS;
    if (component_manager_impl->num_clients == 0) {
        ret = Destroy();
    }
    
    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

int
CmAddComponent(OpenComponentInitializer init_func) {
    CTRACE(("Cm.AddComponent()"));
    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));

    int ret = AddComponent(init_func, NULL, component_manager_impl->pool);

    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

int
CmLoadComponent(const char* path,
                const char* init_func_name) {
    CTRACE(("Cm.LoadComponent(\"%s\", %s())", path, init_func_name));

    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));

    DllHandle lib;
    int ret = LoadLib(&lib, path);
    if (APR_SUCCESS != ret) {
        CTRACE(("failed to load: %d %s\n", ret, path));
        goto load_error;
    }
    
    OpenComponentInitializer init_func;
    ret = GetOpenComponentInitializer(&init_func, lib, init_func_name);
    if (APR_SUCCESS != ret) {
        CTRACE(("failed to init: %d\n", ret));
        goto init_error;
    }

    ret = AddComponent(init_func, lib, lib->pool);
    if (APR_SUCCESS == ret) {
        VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
        return APR_SUCCESS;
    }

    /* ignore errors */
init_error:
    ReleaseLib(lib);
load_error:
    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}

int
CmReleaseComponent(const char* component_name) {
    VERIFY_SUCCESS(apr_thread_rwlock_wrlock(global_lock));
    int ret = RemoveAndFreeComponentInfo(component_name);
    VERIFY_SUCCESS(apr_thread_rwlock_unlock(global_lock));
    return ret;
}