现在已修复。我又添加了一个程序来说明它是如何修复的。该程序用于演示如何在多线程环境中丢失信号。这种信号损失导致竞争条件。阻塞线程永远不会获得解除阻塞的信号，因为它错过了信号。这有条件和互斥量。这类问题的解决方案是使用cond_var。 cond_var保护条件和数据。因此，它将自动锁定条件，并在其他线程发出信号后解除阻塞条件。条件的锁定保护它免受信号未命中的影响。错误的程序 - 竞争条件程序在这里添加。
我有以下程序。我试图通过呼叫解除阻止 - 杀死。但是，我的程序挂起，因为它从不向被阻塞的函数发送信号（）。我不想使用pthread_cond，因为我想在这里演示问题。但是信号没有丢失，但它从未通过信号解锁它。
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <iostream>
/** get pid **/
#include <sys/types.h>
#include <unistd.h>
/** kill signal **/
#include <signal.h>
using namespace std;
int shared_variable = 7;
pid_t pid_A;
pid_t pid_B;
class helium_thread
{
private:
pthread_t *thread_id;
pid_t process_pid;
public:
static pthread_mutex_t mutex_thread;
void set_thread_id(pthread_t tid);
pthread_t *get_thread_id();
int create_thread(pthread_t *thread_ptr, const pthread_attr_t *attr, void * (*start_routine)(void *), void *arg );
helium_thread();
~helium_thread();
};
helium_thread thread_1, thread_2;
void helium_thread::set_thread_id( pthread_t tid)
{
*(this->thread_id) = tid;
}
pthread_t * helium_thread::get_thread_id( )
{
return (this->thread_id);
}
int helium_thread::create_thread(pthread_t *thread_ptr, const pthread_attr_t *attr, void * (*start_routine)(void *), void *arg )
{
int ret;
ret = pthread_create(thread_ptr,attr,start_routine,(void *)arg) ;
cout<<"Thread created "<<std::hex<<thread_ptr<<endl;
return ret;
}
helium_thread::helium_thread()
{
thread_id = new pthread_t;
cout<<"Constructor called "<<std::hex<<thread_id<<endl;
}
helium_thread::~helium_thread()
{
cout<<"Destructor called"<<std::hex<<thread_id<<endl;
delete thread_id;
}
/** While defining the methods of the class, Keywords static and virtual should not be repeated in the definition. **/
/** They should only be used in the class declaration. **/
void *Thread_Function_A(void *thread_arg)
{
int rc = 0;
pthread_mutex_lock(&(helium_thread::mutex_thread));
pid_A = getpid();
cout<<"The pid value of Thread A is"<< pid_A << endl;
if ( shared_variable == 5)
{
shared_variable = 100;
cout<<"The thread A proceeds"<<endl;
pthread_mutex_unlock(&(helium_thread::mutex_thread));
}
else
{ pthread_mutex_unlock(&(helium_thread::mutex_thread));
cout<<"Going to block now"<<endl;
rc = pause();
cout<<"Unblocked now, the rc value is "<<rc<<endl;
}
}
void *Thread_Function_B(void *thread_arg)
{
pthread_mutex_lock(&(helium_thread::mutex_thread));
pid_B = getpid();
cout<<"The pid value of Thread B is"<< pid_B << endl;
shared_variable = 5;
cout<<"Unblock the thread A now"<<endl;
pthread_kill(*(thread_1.get_thread_id()), SIGCONT);
pthread_mutex_unlock(&(helium_thread::mutex_thread));
}
/** The definition of the static member can't be inside a function, You need to put it outside **/
/** When I tried using inside a function, I got the error - error: invalid use of qualified-name ‘helium_thread::mutex_thread **/
pthread_mutex_t helium_thread::mutex_thread = PTHREAD_MUTEX_INITIALIZER;
int main(int argc, char *argv[])
{
pid_t thread_pid_val = getpid();
thread_1.create_thread((thread_1.get_thread_id()),NULL,Thread_Function_A,&thread_pid_val);
thread_2.create_thread((thread_2.get_thread_id()),NULL,Thread_Function_B,&thread_pid_val);
pthread_join( *(thread_1.get_thread_id()), NULL);
pthread_join( *(thread_2.get_thread_id()), NULL);
return 0;
}
输出是 -
$ ./thread_basic.out
Constructor called 0x195c010
Constructor called 0x195c030
Thread created 0x195c010
The pid value of Thread A is404c
Thread created Going to block now
The pid value of Thread B is0x404c
Unblock the thread A now
0x195c030
------------------工作竞赛 - 条件计划 -
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <iostream>
/** get pid **/
#include <sys/types.h>
#include <unistd.h>
/** kill signal **/
#include <signal.h>
using namespace std;
int shared_variable = 7;
pid_t pid_A;
pid_t pid_B;
class helium_thread
{
private:
pthread_t *thread_id;
pid_t process_pid;
public:
static pthread_mutex_t mutex_thread;
void set_thread_id(pthread_t tid);
pthread_t *get_thread_id();
int create_thread(pthread_t *thread_ptr, const pthread_attr_t *attr, void * (*start_routine)(void *), void *arg );
helium_thread();
~helium_thread();
};
helium_thread thread_1, thread_2;
void helium_thread::set_thread_id( pthread_t tid)
{
*(this->thread_id) = tid;
}
pthread_t * helium_thread::get_thread_id( )
{
return (this->thread_id);
}
int helium_thread::create_thread(pthread_t *thread_ptr, const pthread_attr_t *attr, void * (*start_routine)(void *), void *arg )
{
int ret;
ret = pthread_create(thread_ptr,attr,start_routine,(void *)arg) ;
cout<<"Thread created "<<std::hex<<thread_ptr<<endl;
return ret;
}
helium_thread::helium_thread()
{
thread_id = new pthread_t;
cout<<"Constructor called "<<std::hex<<thread_id<<endl;
}
helium_thread::~helium_thread()
{
cout<<"Destructor called"<<std::hex<<thread_id<<endl;
delete thread_id;
}
/** While defining the methods of the class, Keywords static and virtual should not be repeated in the definition. **/
/** They should only be used in the class declaration. **/
void handler(int sig)
{
//do nothing
cout<<"Handler called"<<endl;
}
void *Thread_Function_A(void *thread_arg)
{
int rc = 0;
pthread_mutex_lock(&(helium_thread::mutex_thread));
pid_A = getpid();
cout<<"The pid value of Thread A is"<< pid_A << endl;
while(1)
{
if ( shared_variable == 5)
{
shared_variable = 100;
cout<<"The thread A proceeds"<<endl;
cout<<"The shared_variable value = "<< std::dec<< shared_variable << endl;
pthread_mutex_unlock(&(helium_thread::mutex_thread));
cout<<"The thread exits"<<endl;
pthread_exit(NULL);
}
else
{ pthread_mutex_unlock(&(helium_thread::mutex_thread));
cout<<"Going to block now"<<endl;
/** This sleep will give a sufficient time to schedule thread B **/
/** Once thread B is scheduled, the thread B will sent a signal to unblock the thread A **/
/** The signal has been sent, but this thread was not in the pause instruction **/
sleep(5);
cout<<"Sleep completed now"<<endl;
/** Thread B has sent the signal; and it may be lost **/
/** The pause will be blocked now, waiting for the signal to occur again **/
rc = pause();
cout<<"Unblocked now, the rc value is "<<rc<<endl;
}
}
}
void *Thread_Function_B(void *thread_arg)
{
pthread_mutex_lock(&(helium_thread::mutex_thread));
pid_B = getpid();
cout<<"The pid value of Thread B is"<< pid_B << endl;
shared_variable = 5;
cout<<"Unblock the thread A now"<<endl;
pthread_kill(*(thread_1.get_thread_id()), SIGUSR1);
pthread_mutex_unlock(&(helium_thread::mutex_thread));
cout<<"Return thread function b now"<<endl;
}
/** The definition of the static member can't be inside a function, You need to put it outside **/
/** When I tried using inside a function, I got the error - error: invalid use of qualified-name ‘helium_thread::mutex_thread **/
pthread_mutex_t helium_thread::mutex_thread = PTHREAD_MUTEX_INITIALIZER;
int main(int argc, char *argv[])
{
pid_t thread_pid_val = getpid();
/** Install signal handler **/
signal(SIGUSR1, handler);
thread_1.create_thread((thread_1.get_thread_id()),NULL,Thread_Function_A,&thread_pid_val);
thread_2.create_thread((thread_2.get_thread_id()),NULL,Thread_Function_B,&thread_pid_val);
pthread_join( *(thread_1.get_thread_id()), NULL);
pthread_join( *(thread_2.get_thread_id()), NULL);
return 0;
}
输出如下。
$ ./thread_basic.out
Constructor called 0x1e01010
Constructor called 0x1e01030
Thread created 0x1e01010
The pid value of Thread A is45a6
Going to block now
Thread created 0x1e01030
The pid value of Thread B is45a6
Unblock the thread A now
Return thread function b now
Handler called
Sleep completed now
答案 0 :(得分：1)
您应该使用pthread_t t_a = pthread_self()代替getpid()
而pthread_kill(t_a , SIGCONT)代替kill
SIGCONT仅继续之前由SIGSTOP或SIGTSTP
所以，您可能想尝试：
pthread_kill(pthread_self(), SIGSTOP);
而不是pause()
POSIX线程有条件变量是有原因的;使用它们......
答案 1 :(得分：1)
添加信号处理程序。
void handler(int sig)
{
//do nothing
}
从main（或某处）设置它以捕获SIGUSR1（或类似的）
signal(SIGUSR1, handler);
ThreadB调用
pthread_kill(pthread_self(), SIGUSR1);
将运行信号处理程序，pause将唤醒并返回-1并继续。
这会起作用，但仍然非常尴尬。
答案 2 :(得分：0)
kill向进程发送信号，并且如您的输出所示，您的两个线程都属于同一进程。您需要使用pthread_kill或特定于Linux的tkill或使用pthread_sigmask，以确保只有暂停的线程接收SIGCONT信号。