最近在進行利用socket將一個topic上的位姿消息發送給UR5機器人的實驗。由於socket時刻都處於接聽的狀態,類似一個死循環,另外由於只要接聽的topic上一有消息來,就會調用callback函數,所以消息不斷來時,這裏也相當於一個死循環。因此就老運行不了。因此想到了使用一個多線程來進行這兩部分的工作。
由於在qtcreator裏面進行編譯,所以使用QThread類來進行。下面就來說明一下。
我的node接聽了一個其他node來的topic,在callback函數中,我將接聽來的值給六個變量賦值。socket再讀取這六個變量,將它進行一定處理後發送給UR5的控制器,使UR5進行運動。
下面時socket.h頭文件:
#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
在頭文件中,我們聲明一個類QtROS,讓他繼承QThread。裏面包括:構造函數,析構函數,實例化一個句柄,一個socket的函數,一個run()。這個run函數極其重要,多線程中,QThread有一個槽函數start(),當觸發它時,就會自動跳到run函數中進行執行。這裏的Q_OBJECT要註釋掉,否則用catkin_make編譯時,會提示
/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
的錯誤。具體原因設計到qt的編譯原理,這裏就不詳述了。當然有它也可在CMakeLists.txt中進行一些QT的宏設置來進行編譯。
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 //客戶端的最大數量
using namespace std;
struct sockaddr_in Client;
//int ursocket();
int ListenSocket; //創建的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); //等待指定的端口出現客戶端連接
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);//用於接受客戶端的請求
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={},否則會出現末尾亂碼的現象。
char back[100]={0};
cout<<"time "<<i<<endl;
optimizer_mutex_.lock();//試圖鎖住互斥量,如果另一個線程已經鎖住了這個互斥量,那麼這次調用將阻塞知道那個線程把它解鎖
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();
}
這裏就是對頭文件中的函數進行定義,int QtROS::ursocket()中進行socket的創建、綁定、接聽。QtROS::QtROS(int argc, char *argv[], const char* node_name)中進行一些ROS的初始化,這裏主要是說明生成的node。重要的是run函數中,一直在accept,接受請求、發送數據。
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" //用雙引號,否則用<>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試圖鎖住互斥量,沒有鎖住返回false。這裏就是:如果被鎖住。。。
{
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();//試圖鎖住互斥量,如果另一個線程已經鎖住了這個互斥量,那麼這次調用將阻塞知道那個線程把它解鎖
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函數中的處理。首先,實例化一個 QtROS對象qtros,並說明生成的node名字爲socket_to_ur5_node。然後實例化一個QCoreApplication對象。實例化訂閱器訂閱topic,並在callback函數中將接受的位姿進行賦值。
這裏會出現的問題是segment fault ,core dump的錯誤。原因就是callback函數對Jvalue0~Jvalue5進行訪問寫值時,run函數又在讀取這些值進行發送,所以就出現了這個錯誤。因此,我們在兩個地方的Jvalue0~Jvalue5處要進行互鎖操作,這就涉及到QT中類QThread的使用。這個類的成員函數如下:
最重要的是lock (),tryLock ()和unlock ()的使用。
tryLock ()試圖鎖住互斥量(自己可以訪問,其他線程不能訪問),如果這裏已經被其他線程鎖住了,那麼他就沒有鎖住,返回false。
lock()鎖住互斥量,如果被其他線程鎖住(正被另一個線程訪問),那就等待,直到被解鎖。
unlock()就是這個線程完成對中間這段程序的讀寫之後,進行解鎖。
所以我們在上面兩個地方用這三個函數,確保同時只有一個線程對其進行訪問和讀寫。