In the Linux top and PS commands, the default is to see the PID (Process id), perhaps you can see the LWP (thread id) and Tgid (thread group ID for the thread group leader), and so on, while the Li Nux library functions and system calls maybe you noticed the Pthread ID and the TID, and so on. There are more IDs, such as PGRP (process group ID), sid (session ID for the session leader) and Tpgid (TTY process group ID for the process GR OUP leader). Too many concepts may be faint, but as long as you have an accurate understanding of the basic concepts of Linux processes and threads, the meanings of these IDs are solved. The core concepts of processes and threads are described below, and the relationships between these IDs are validated with a sample program.
Linux processes and threads have a lot of similarities and differences, can be under Google. But as long as you can clearly understand the points, it is enough to understand the meaning of the various IDs in Linux.
The 1th note above is the most basic and most important.
Initial understanding of the various IDs. Basically, from high to low, IDs below the split line are less important.
As you can see from the list above, the various IDs are finally attributed to the PID and LWP (TID). So understanding the various IDs ultimately boils down to understanding the connections and differences between PID and LWP (TID) .
The following figure is a diagram that describes the relationship between a parent-child process and a thread.
A good description of user view and kernel view (kernel view) See the difference between threads:
It is important to note that sometimes the process and thread distinctions in Linux are not very strict. Even if the threads and processes are mixed, the PID and TID mix, depending on the context, can still clearly distinguish the meaning of the other person wants to express. , from the kernel perspective to see the PID 44, is from the point of view of the dispatch unit, but in the top or PS command, you can absolutely not find a PID 44 process, only see an LWP (TID) is a 44 thread.
A sample program is used to further understand the PID and LWP (TID) and to print out various IDs using the formatted PS command. The following program creates 2 sub-threads in the main function, plus the main thread, which has a total of 3 threads. Verify the relationship between the PID and the LWP (TID) by printing the Pthread ID, PID, and LWP (TID) separately in 3 threads.
#include <unistd.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <pthread.h>
#define gettidv1() syscall(__NR_gettid) // new form
#define gettidv2() syscall(SYS_gettid) // traditional form
void *ThreadFunc1()
{
printf("the pthread_1 id is %ld\n", pthread_self());
printf("the thread_1's Pid is %d\n", getpid());
printf("The LWPID/tid of thread_1 is: %ld\n", (long int)gettidv1());
pause();
return 0;
}
void *ThreadFunc2()
{
printf("the pthread_2 id is %ld\n", pthread_self());
printf("the thread_2's Pid is %d\n", getpid());
printf("The LWPID/tid of thread_2 is: %ld\n", (long int)gettidv1());
pause();
return 0;
}
int main(int argc, char *argv[])
{
pid_t tid;
pthread_t pthread_id;
printf("the master thread's pthread id is %ld\n", pthread_self());
printf("the master thread's Pid is %d\n", getpid());
printf("The LWPID of master thread is: %ld\n", (long int)gettidv1());
// Create 2 threads pthread_create(&pthread_id, NULL, ThreadFunc2, NULL);
pthread_create(&pthread_id, NULL, ThreadFunc1, NULL);
pause();
return 0;
}
Note that when compiling, you use-l to specify the library parameters.
gcc threadtest.c-o threadtest-l pthread
Execute the procedure with the following results:
# ./threadTest the master thread's pthread id is 140154481125184 the master thread's Pid is 20992 The LWPID of master thread is: 20992 the pthread_1 id is 140154464352000 the thread_1's Pid is 20992 The LWPID/tid of thread_1 is: 20994 the pthread_2 id is 140154472744704 the thread_2's Pid is 20992 The LWPID/tid of thread_2 is: 20993
The above results indicate that the Pthread ID is the ID provided by the Pthread library and has no meaning at the system level. The PID is the process ID of the thread group leader, which is 20992. The LWP (TID) is the thread ID, which is 20993 and 20994, respectively.
While using PS to view the results, note that PS defaults to printing only process-level information and requires the-l option to view the thread's basic information.
# ps -eo pid,tid,lwp,tgid,pgrp,sid,tpgid,args -L | awk '{if(NR==1) print $0; if($8~/threadTest/) print $0}'
PID TID LWP TGID PGRP SID TPGID COMMAND
20992 20992 20992 20992 20992 30481 20992 ./threadTest
20992 20993 20993 20992 20992 30481 20992 ./threadTest
20992 20994 20994 20992 20992 30481 20992 ./threadTest
From the above results, you can see:
The default top displays the number of tasks, which is the process.
You can switch to a thread by tapping "H". As you can see, there are actually 96 threads. You can also use the top-h command directly to print thread conditions directly.
The-l option of PS can be used to see threads and can usually print out information about LWP and NLWP. You can view the thread information as follows:
PS -elf
pidstat-t [-P PID number] can print the relationship between the threads.
To enable thread viewing in Htop, turn on htop and press <F2> to enter the Htop settings menu. Select display options under the Settings bar, and then turn on the tree view and show custom thread names options. Press <F10> to exit settings.
Note: Mac's F2 press FN+F2.
The difference between a Linux process and a thread
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