C++ gettid() was not declared in this scope

Question

A simple program is: I would like to get the thread ID of both of the threads using this gettid function. I do not want to do the sysCall directly. I want to use this function.

#include <iostream>
#include <boost/thread/thread.hpp>
#include <boost/date_time/date.hpp>
#include <unistd.h>
#include <sys/types.h>
using namespace boost;
using namespace std;

boost::thread thread_obj;
boost::thread thread_obj1;

void func(void)
{
    char x;
    cout << "enter y to interrupt" << endl;
    cin >> x;
     pid_t tid = gettid();
    cout << "tid:" << tid << endl;
    if (x == 'y') {
        cout << "x = 'y'" << endl;    
        cout << "thread interrupt" << endl;
    }
}

void real_main() {

   cout << "real main thread" << endl;
    pid_t tid = gettid();
    cout << "tid:" << tid << endl;

    boost::system_time const timeout = boost::get_system_time() + boost::posix_time::seconds(3);
    try {
        boost::this_thread::sleep(timeout);
    }
    catch (boost::thread_interrupted &) {
        cout << "thread interrupted" << endl;
    }

}

int main()
{
    thread_obj1 = boost::thread(&func);
    thread_obj = boost::thread(&real_main);
    thread_obj.join();
}

It gives Error on compilation; The use of gettid() has been done according to the man page:

$g++ -std=c++11 -o Intrpt Interrupt.cpp -lboost_system -lboost_thread
Interrupt.cpp: In function ‘void func()’:
Interrupt.cpp:17:25: error: ‘gettid’ was not declared in this scope
      pid_t tid = gettid();

score 44 · Answer 1 · edited Sep 01 '16 at 14:09

44

This is a silly glibc bug. Work around it like this:

#include <unistd.h>
#include <sys/syscall.h>
#define gettid() syscall(SYS_gettid)

edited Sep 01 '16 at 14:09

Flow

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answered Mar 16 '16 at 01:08

Glenn Maynard

55,829
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3

that's not a bug, man-page states that, see answer https://stackoverflow.com/a/30681498/142561 – zowers Oct 17 '18 at 08:59
2

was fixed in glibc 2.30 – sqr163 Mar 26 '19 at 01:48
Describing buggy behavior doesn't make it not a bug, it just makes it an acknowledged bug. Glad it was fixed. – Glenn Maynard Jun 30 '22 at 06:13

score 7 · Answer 2 · edited Jun 20 '20 at 09:12

7

The man page you refer to can be read online here. It clearly states:

Note: There is no glibc wrapper for this system call; see NOTES.

and

NOTES

Glibc does not provide a wrapper for this system call; call it using syscall(2).

The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).

So you can't. The only way to use this function is through the syscall.

But you probably shouldn't anyway. You can use pthread_self() (and compare using pthread_equal(t1, t2)) instead. It's possible that boost::thread has its own equivalent too.

edited Jun 20 '20 at 09:12

Community

1
1

answered Jun 06 '15 at 10:04

5

There's nothing "clearly stated" about saying "there's no glibc wrapper". – Glenn Maynard Mar 16 '16 at 01:07
1

was fixed in glibc 2.30 – sqr163 Mar 26 '19 at 01:48

score 6 · Answer 3 · answered Aug 19 '20 at 20:47

Additional to the solution provided by Glenn Maynard it might be appropriate to check the glibc version and only if it is lower than 2.30 define the suggested macro for gettid().

#if __GLIBC__ == 2 && __GLIBC_MINOR__ < 30
#include <sys/syscall.h>
#define gettid() syscall(SYS_gettid)
#endif

C++ gettid() was not declared in this scope

3 Answers3

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