android + pthread + c++ = SIGSEGV

Question

The following code compiles and runs on standard linux:

#include <iostream>
#include <pthread.h>

using namespace std;

class Foo
{
    public:
        Foo();
        void go_thread();
        void stop_thread();
    private:
        static void* worker( void* param );
        pthread_t m_pt;
};

Foo::Foo()
{
    m_pt = 0;
}

void Foo::go_thread()
{
    int success = pthread_create( &m_pt, NULL, worker, static_cast<void*>(this) );

    if( success == 0 )
    {
        cout << "thread started" << endl;
    }
}

void Foo::stop_thread()
{
    int success = pthread_join( m_pt, NULL );

    if( success == 0 )
    {
        cout << "thread stopped" << endl;
    }
}

void* Foo::worker( void* p )
{
    cout << "thread running" << endl;
    return 0;
}

int main()
{
    Foo f;
    f.go_thread();
    f.stop_thread();
    return 0;
}

and produces the following output:

$ ./a.out
thread started
thread running
thread stopped
$

This code also builds with the Android NDK (r5b). However, when I adb push the resulting executable to a device and run it, I get a SIGSEGV before main() even runs. I've isolated the issue down to pthread_create() It seems the mere existence of this call in my code, never mind execution, causes my prog to seg fault. Any ideas?

Answer 1

It may not be this but try making the function called by pthread create a normal c-function (ie declare it as extern "C") not a static member function:

This is because technically the calling convention for static members may be different from the C calling convention that is used by the C-library pthread (though a lot of the times they are the same (which is why it works on your linux box) in my opinion it is not worth the porting risk).

extern "C" void* start_the_thread(void*);

void* start_the_thread(void* data)
{
    Foo*  theObject = static_cast<Foo*>(data);
    // In Java if your Foo had been derived from Runable
    // This is s where theObject->run() would have been called.
    return Foo::worker(data);
}

int success = pthread_create( &m_pt, NULL, start_the_thread, static_cast<void*>(this)

Answer 2

The issue seems to be combining iostream with pthread. I went through and replaced all couts with printf()s, removed the using clause, and removed the iostream header. The code compiled and ran with no issue on the device. I wonder if this is something Google should be made aware of?

The final (working) code looks like:

#include <pthread.h>
#include <stdio.h>

class Foo
{
    public:
        Foo();
        void go_thread();
        void stop_thread();
    private:
        static void* worker( void* param );
        pthread_t m_pt;
};

Foo::Foo()
{
    m_pt = 0;
}

void Foo::go_thread()
{
    int success = pthread_create( &m_pt, NULL, worker, static_cast<void*>(this) );

    if( success == 0 )
    {
        printf( "thread started\n" );
    }
}

void Foo::stop_thread()
{
    int success = pthread_join( m_pt, NULL );

    if( success == 0 )
    {
        printf( "thread stopped\n" );
    }
}

void* Foo::worker( void* p )
{
    printf( "thread running\n" );
    return 0;
}

int main()
{
    Foo f;
    f.go_thread();
    f.stop_thread();
    return 0;
}