- 优点
这个模块类的,为其他模块提供了很方便的入口,简化了我们的代码,同时,提供了安全的start/stop的静态方法.
- 缺点
这个模板类仅仅支持单实例(不实用在mavlink中)
px4_module.h学习
1.查看px4_module.h的历史提交记录
$ git log px4_module.h
commit 04c4339ca3a026e682412946fdc5e554c94e19f7
Author: Beat Küng <beat-kueng@gmx.net>
Date: Thu Apr 27 17:00:03 2017 +0200
2. 类方法说明
extern pthread_mutex_t px4_modules_mutex;
template<class T>
class ModuleBase
{
public:
ModuleBase() = default;
virtual ~ModuleBase() {}
//单个线程的实例的入口就是这个modulebase的静态main的入口
static int main(int argc, char *argv[])
{
if (argc <= 1 || strcmp(argv[1], "help") == 0 || strcmp(argv[1], "-h") == 0) {
return T::print_usage();
}
//start用来创建线程的实例, 同时会创建线程入口
if (strcmp(argv[1], "start") == 0) {
return start_command_base(argc - 1, argv + 1);
}
//杀死线程,销毁资源
if (strcmp(argv[1], "stop") == 0) {
return stop_command();
}
//查询状态
if (strcmp(argv[1], "status") == 0) {
return status_command();
}
//执行用户命令
lock_module(); // we better lock here, as the method could access _object
int ret = T::custom_command(argc - 1, argv + 1);
unlock_module();
return ret;
}
static int run_trampoline(int argc, char *argv[])
{
int ret = 0;
_object = T::instantiate(argc, argv);
if (_object) {
T *object = (T *)_object;
object->run();
} else {
PX4_ERR("failed to instantiate object");
ret = -1;
}
exit_and_cleanup();
return ret;
}
//线程入口的创建
static int start_command_base(int argc, char *argv[])
{
int ret = 0;
lock_module();
if (is_running()) {
ret = -1;
PX4_ERR("Task already running");
} else {
ret = T::task_spawn(argc, argv);
if (ret < 0) {
PX4_ERR("Task start failed (%i)", ret);
}
}
unlock_module();
return ret;
}
//杀死线程,同时释放线程的资源
static int stop_command()
{
int ret = 0;
lock_module();
if (is_running()) {
if (_object) {
T *object = (T *)_object;
object->request_stop();
unsigned int i = 0;
do {
unlock_module();
usleep(20000); // 20 ms
lock_module();
if (++i > 100 && _task_id != -1) { // wait at most 2 sec
if (_task_id != task_id_is_work_queue) {
px4_task_delete(_task_id);
}
_task_id = -1;
if (_object) {
delete _object;
_object = nullptr;
}
ret = -1;
break;
}
} while (_task_id != -1);
} else {
// very unlikely event and can only happen on work queues:
// the starting thread does not wait for the work queue to initialize,
// and inside the work queue, the allocation of _object fails
// and exit_and_cleanup() is not called.
_task_id = -1;
}
}
unlock_module();
return ret;
}
// status是打印线程的状态
static int status_command()
{
int ret = -1;
lock_module();
if (is_running() && _object) {
T *object = (T *)_object;
ret = object->print_status();
} else {
PX4_INFO("not running");
}
unlock_module();
return ret;
}
//子类需要实现这个虚函数, 线程的入口
virtual void run() {}
//这里是判断线程是否执行的方法: 通过任务id进行判断
static bool is_running() { return _task_id != -1; }
protected:
// there will be one instance for each template type
static volatile T *_object; ///< instance if the module is running
static int _task_id; ///< task handle: -1 = invalid, otherwise task is assumed to be running
};
//静态变量初始化, _object和_task_id
template<class T>
volatile T *ModuleBase<T>::_object = nullptr;
template<class T>
int ModuleBase<T>::_task_id = -1;
3. logger使用modulebase的例子
class Logger : public ModuleBase<Logger>
{
public:
Logger(LogWriter::Backend backend, size_t buffer_size, uint32_t log_interval, const char *poll_topic_name,
bool log_on_start, bool log_until_shutdown, bool log_name_timestamp, unsigned int queue_size);
~Logger();
/** @see ModuleBase */
static int task_spawn(int argc, char *argv[]);
/** @see ModuleBase */
static Logger *instantiate(int argc, char *argv[]);
/** @see ModuleBase */
static int custom_command(int argc, char *argv[]);
/** @see ModuleBase */
static int print_usage(const char *reason = nullptr);
/** @see ModuleBase::run() */
void run() override;
/** @see ModuleBase::print_status() */
int print_status() override;
//logger线程
int logger_main(int argc, char *argv[])
-> return Logger::main(argc, argv);
->static int main(int argc, char *argv[]) //modulesbase 静态函数
-> static int start_command_base(int argc, char *argv[]) //静态函数
-> ret = T::task_spawn(argc, argv);
-> _task_id = px4_task_spawn_cmd("logger",
->static int run_trampoline(int argc, char *argv[]) //静态函数
-> _object = T::instantiate(argc, argv); //用户的实例入口
//解析输入的参数
->while ((ch = px4_getopt(argc, argv, "r:b:etfm:q:p:", &myoptind, &myoptarg)) != EOF) {
->if (_object) {
//执行周期的处理
->object->run();
//子类继承ModuleBase
class Logger : public ModuleBase<Logger>
{
public:
Logger(LogWriter::Backend backend, size_t buffer_size, uint32_t log_interval, const char *poll_topic_name,
bool log_on_start, bool log_until_shutdown, bool log_name_timestamp, unsigned int queue_size);
~Logger();
//子类 实现run周期性方法
void run() override;
//子类 实现打印的
int print_status() override;