GDB is showing 1 Thread in non threaded application

Question

I was debugging my app with gdb. I used break main So it can break when main is called. Know if I use thread info it shows that thread count is 1.

How a thread is starting before main ? I don't have any thread call in my call so from where thread is getting created. I am using these libs

sqlite , curl , pcre , c-client

Update I have written a sample program to test that if all program start with single thread

 #include<iostream>
int main(int argc,char *argv[]){
  std:: cout<<"Will I have any thread";
  return 0;
}

but when I debug it with gdb

    (gdb) break main
Breakpoint 1 at 0x400783: file threadtest.cpp, line 3.
(gdb) run
Starting program: /home/vivek/Desktop/a.out 

Breakpoint 1, main (argc=1, argv=0x7fffffffe728) at threadtest.cpp:3
3         std:: cout<<"Will I have any thread";
(gdb) info threads
* 1 process 21608  main (argc=1, argv=0x7fffffffe728) at threadtest.cpp:3
(gdb)

it doesn't show the same information. It show 1 process not 1 thread.

When I compile it with -lpthread it show 1 thread.

So program start with one thread when we use lpthread ? or GDB behaves like that ?

Could it be, that this thread is your main thread?

p4553d
– p4553d

2011-02-25 09:59:00 +00:00
Commented Feb 25, 2011 at 9:59 — p4553d
– p4553d, Commented Feb 25, 2011 at 9:59

Maister · Accepted Answer · 2011-02-25 09:58:13Z

2

All programs have at least 1 thread, the main thread. The program is started before main since the C++ runtime does some initializing before main() starts, like calling all global objects which have constructors.

answered Feb 25, 2011 at 9:58

Maister

5,0641 gold badge34 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Vivek Goel Over a year ago

When I use -lpthread for linking in sample program gdb show 1 thread. But when not it show one process. So program start with one thread when we use lpthread ? or GDB behaves like that ?

Stack Overflow is garbage Over a year ago

There is always a thread (the main thread, as @Maister mentioned) within a process. But GDB can't tell you anything about threads unless you link with a threading library.

user · Accepted Answer · 2011-02-25 09:58:44Z

1

The operating system creates a process space with one thread and calls the application loader to execute the application in that thread, which in turns performs some initial setup (gathering command line arguments into argc and argv, for example) and calls main.

answered Feb 25, 2011 at 9:58

user

6,9478 gold badges47 silver badges82 bronze badges

Comments

Vivek Goel · Accepted Answer · 2011-02-25 10:08:26Z

0

For the sample App when I compile it with -lpthread it shows 1 thread is running. So lpthread is playing key point here.

 (gdb) break main
Breakpoint 1 at 0x400793: file threadtest.cpp, line 3.
(gdb) run
Starting program: /home/vivek/Desktop/a.out 
[Thread debugging using libthread_db enabled]

Breakpoint 1, main (argc=1, argv=0x7fffffffe728) at threadtest.cpp:3
3         std:: cout<<"Will I have any thread";
(gdb) info threads
* 1 Thread 0x2aaaaaac8bb0 (LWP 21649)  main (argc=1, argv=0x7fffffffe728)
    at threadtest.cpp:3
(gdb)

answered Feb 25, 2011 at 10:08

Vivek Goel

24.4k30 gold badges119 silver badges194 bronze badges

Collectives™ on Stack Overflow

GDB is showing 1 Thread in non threaded application

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related