最近在进行利用socket将一个topic上的位姿消息发送给UR5机器人的实验。由于socket时刻都处于接听的状态,类似一个死循环,另外由于只要接听的topic上一有消息来,就会调用callback函数,所以消息不断来时,这里也相当于一个死循环。因此就老运行不了。因此想到了使用一个多线程来进行这两部分的工作。
由于在qtcreator里面进行编译,所以使用QThread类来进行。下面就来说明一下。
我的node接听了一个其他node来的topic,在callback函数中,我将接听来的值给六个变量赋值。socket再读取这六个变量,将它进行一定处理后发送给UR5的控制器,使UR5进行运动。
下面时socket.h头文件:
#ifndef SOCKET_H
#define SOCKET_H
#include "ros/ros.h"
#include <qt4/QtGui/QApplication>
#include <qt4/QtCore/QCoreApplication>
#include <qt4/QtCore/QObject>
#include <qt4/QtCore/QThread>
//about socket
#include <stdio.h>
#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <cerrno>
#include <cstring>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <csignal>
#include <qt4/QtCore/QMutex>
class QtROS:public QThread
{
//Q_OBJECT
public:
QtROS(int argc, char *argv[], const char* node_name);
virtual ~QtROS();
//ros::NodeHandle getNodeHandle(){return *n;}
int ursocket();
void run();
private:
//ros::NodeHandle* n;
};
#endif // SOCKET_H
在头文件中,我们声明一个类QtROS,让他继承QThread。里面包括:构造函数,析构函数,实例化一个句柄,一个socket的函数,一个run()。这个run函数极其重要,多线程中,QThread有一个槽函数start(),当触发它时,就会自动跳到run函数中进行执行。这里的Q_OBJECT要注释掉,否则用catkin_make编译时,会提示
/home/congleetea/catkin_ws/src/socket_to_ur5/src/socket.cpp:-1: error: undefined reference to `vtable for QtROS'
:-1: error: collect2: ld returned 1 exit status
的错误。具体原因设计到qt的编译原理,这里就不详述了。当然有它也可在CMakeLists.txt中进行一些QT的宏设置来进行编译。
下面是socket.cpp文件:
#include "ros/ros.h"
#include "std_msgs/String.h"
#include "moveit_msgs/RobotTrajectory.h"
#include "socket.h"
#include <qt4/QtCore/QThread>
#define PORT 30002
#define HOSTIP "192.168.0.100"
#define MAXDATESIZE 100
#define BACKLOG 5 //客户端的最大数量
using namespace std;
struct sockaddr_in Client;
//int ursocket();
int ListenSocket; //创建的socket返回的
int ConnectSocket;
int bindit;
int listento;
struct sockaddr_in server; //my address information
struct sockaddr_in Client_addr; //address information of connected machine
int sin_size = sizeof(sockaddr_in);
extern float Jvalue0;
extern float Jvalue1;
extern float Jvalue2;
extern float Jvalue3;
extern float Jvalue4;
extern float Jvalue5;
extern QMutex optimizer_mutex_;
QtROS::QtROS(int argc, char *argv[], const char* node_name)
{
std::cout << "Initializing Node...\n";
ros::init(argc, argv, node_name);
// n = new ros::NodeHandle(node_name); //Use node name as Ros Namespace
ROS_INFO("Connected to roscore");
}
QtROS::~QtROS()
{
}
int QtROS::ursocket()
{
cout<<"welcome to socket!"<<endl;
memset(&server,0,sin_size);//初始化
//create socket
ListenSocket = socket(AF_INET, SOCK_STREAM, 0);
if(ListenSocket == -1) //if call socket fail
{
cout<<"Error socket"<<strerror(errno)<<endl;
exit(1);
}
cout<<"socket is ok"<<endl;
//bind socket
server.sin_family = AF_INET; // host byte order , AF_INET = IPv4 Internet Protocols for Linux
server.sin_port = htons(PORT); // sin_port is in short-network byte order,htons()=converts PORTNUMBER to network byte order
server.sin_addr.s_addr = inet_addr(HOSTIP); // use my address automatically, use "INADDR_ANY"(0 so no need htons) or "inet_addr("192.120.13.1")
memset(&(server.sin_zero), '\0', sin_size);
//assign the address specified to the socket
bindit = bind(ListenSocket, (struct sockaddr *)&server, sin_size);
if (bindit == -1)
{//error check for bind()
cout <<"error bindit, because"<< strerror(errno)<<endl;
exit(1);
}
else
cout<<"bind is ok"<<endl;
//listen socket
listento = listen(ListenSocket, BACKLOG); //等待指定的端口出现客户端连接
if (listento == -1)
{//error check for listen()
cout <<"error listento, bacause "<< strerror(errno)<<endl;
exit(1);
}
cout<<"listen is ok!"<<endl;
return 0;
}
void QtROS::run()
{
int i=1;
ursocket();
while(ros::ok())
{
//accept a connection on listened socket
ConnectSocket = accept(ListenSocket, (struct sockaddr *)&Client_addr, (socklen_t*)&sin_size);//用于接受客户端的请求
if (ConnectSocket == -1)
{//error check for accept()
cout << "accept() has failed! because " << strerror(errno) << endl;
close(ConnectSocket);
}
cout << "Server_addr: got connection from " << inet_ntoa(Client_addr.sin_addr) << endl;
char pose[100]={0};
char movesign[100]={0}; //最好初始化={},否则会出现末尾乱码的现象。
char back[100]={0};
cout<<"time "<<i<<endl;
optimizer_mutex_.lock();//试图锁住互斥量,如果另一个线程已经锁住了这个互斥量,那么这次调用将阻塞知道那个线程把它解锁
cout<<"it is locked by socket"<<endl;
sprintf(pose,"(%.5f,%.5f,%.5f,%.5f,%.5f,%.5f)", Jvalue0,Jvalue1,Jvalue2,Jvalue3,Jvalue4,Jvalue5);
optimizer_mutex_.unlock();
cout<<"pose is :"<<pose<<endl;
recv(ConnectSocket,movesign,100,0);
cout<<"movesign is:"<<movesign<<endl;
if(movesign[0]=='a')
{
if(send(ConnectSocket,pose,100,0) == -1)
{
printf("write fail!\r\n");
}
printf("send ok!\r\n");
recv(ConnectSocket,back,100,0);
cout<<"back is :"<<back<<endl;
}
else
break;
close(ConnectSocket);
i++;
}
close(ListenSocket);
ros::spin();
}
这里就是对头文件中的函数进行定义,int QtROS::ursocket()中进行socket的创建、绑定、接听。QtROS::QtROS(int argc, char *argv[], const char* node_name)中进行一些ROS的初始化,这里主要是说明生成的node。重要的是run函数中,一直在accept,接受请求、发送数据。
下面是main.cpp:
#include "ros/ros.h"
#include "std_msgs/String.h"
#include "moveit_msgs/RobotTrajectory.h"
#include <qt4/QtCore/QObject>
#include <qt4/QtCore/QThread>
#include "socket.h" //用双引号,否则用<>可能找不到
using namespace std;
//class QtROS;
float Jvalue0 ;
float Jvalue1 ;
float Jvalue2 ;
float Jvalue3 ;
float Jvalue4 ;
float Jvalue5 ;
QMutex optimizer_mutex_;
void chatterCallback(const moveit_msgs::RobotTrajectory msg )//std_msgs::String::ConstPtr& msg
{
if(optimizer_mutex_.tryLock())//tryLock试图锁住互斥量,没有锁住返回false。这里就是:如果被锁住。。。
{
for(int i = 0; i < msg.joint_trajectory.points.size(); i++)
{
trajectory_msgs::JointTrajectoryPoint tra = msg.joint_trajectory.points[i];
Jvalue0 = tra.positions[0];
Jvalue1 = tra.positions[1];
Jvalue2 = tra.positions[2];
Jvalue3 = tra.positions[3];
Jvalue4 = tra.positions[4];
Jvalue5 = tra.positions[5];
cout<<"Jvalue0~5: "<<Jvalue0<<" "<<Jvalue1<<" "<<Jvalue2<<" "<<Jvalue3<<" "<<Jvalue4<<" "<<Jvalue5<<endl;
}
cout<<"it is finished"<<endl;
optimizer_mutex_.unlock();//试图锁住互斥量,如果另一个线程已经锁住了这个互斥量,那么这次调用将阻塞知道那个线程把它解锁
cout<<"it is unlocked"<<endl;
return;
}
cout<<"it is locked by main"<<endl;
cout<<"it is unlocked"<<endl;
return ;
}
int main(int argc, char **argv)
{
QtROS qtros(argc, argv, "socket_to_ur5_node");
QCoreApplication a(argc, argv);
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("/robot_trajectory", 100, chatterCallback);
qtros.start();
ros::spin();
a.exec();
}
重要的是main函数中的处理。首先,实例化一个 QtROS对象qtros,并说明生成的node名字为socket_to_ur5_node。然后实例化一个QCoreApplication对象。实例化订阅器订阅topic,并在callback函数中将接受的位姿进行赋值。
这里会出现的问题是segment fault ,core dump的错误。原因就是callback函数对Jvalue0~Jvalue5进行访问写值时,run函数又在读取这些值进行发送,所以就出现了这个错误。因此,我们在两个地方的Jvalue0~Jvalue5处要进行互锁操作,这就涉及到QT中类QThread的使用。这个类的成员函数如下:
最重要的是lock (),tryLock ()和unlock ()的使用。
tryLock ()试图锁住互斥量(自己可以访问,其他线程不能访问),如果这里已经被其他线程锁住了,那么他就没有锁住,返回false。
lock()锁住互斥量,如果被其他线程锁住(正被另一个线程访问),那就等待,直到被解锁。
unlock()就是这个线程完成对中间这段程序的读写之后,进行解锁。
所以我们在上面两个地方用这三个函数,确保同时只有一个线程对其进行访问和读写。