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To: <cygwin@cygwin.com>
Subject: AF_UNIX/SOCK_DGRAM is dropping messages
Date: Tue, 23 Mar 2021 16:37:52 +0100
Message-ID: <04cc01d71ffa$7d1e6cf0$775b46d0$@gmail.com>
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From: Kristian Ivarsson via Cygwin <cygwin@cygwin.com>
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Hi all

Using AF_UNIX/SOCK_DGRAM with current version (3.2.0) seems to drop =
messages or at least they are not received in the same order they are =
sent

Attached C:ish (with C++ threads though) sample program that essentially =
creates a "client" that writes as much as possible and a "server" that =
consumes as much as possible

It seems like some buffer is filled and then messages are dropped (or at =
least it appears so) (if someone is about to test this, the "sleep" =
might need to be adjusted in order to make this happen)

Hopefully it's just a flaw in our application (and sample), but as far =
as we can see, this should work


Does anyone, perhaps named Ken, have any insightful thoughts about this =
?


Best regards,
Kristian

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	filename="af_unix.cpp"

#include <sys/socket.h>
#include <sys/un.h>

#include <unistd.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <thread>
#include <chrono>


// $ g++ --std=3Dgnu++17 af_unix.cpp

const char* const path =3D "address";
const int count =3D 1000;
const int size =3D BUFSIZ * 2;

int client()
{
    const int fd =3D socket( AF_UNIX, SOCK_DGRAM, 0);

    if( fd =3D=3D -1)
    {
        perror( "socket error");
        return -1;
    }

    struct sockaddr_un address{};

    strcpy( address.sun_path, path);
    address.sun_family =3D AF_UNIX;

    char buffer[size] =3D {};

    for( int idx =3D 0; idx < count; ++idx)
    {
        memcpy( buffer, &idx, sizeof idx);

        const ssize_t result =3D sendto( fd, buffer, size, 0, (struct =
sockaddr*)&address, sizeof address);

        if( result =3D=3D -1)
        {
            perror( "sendto error");
            return -1;
        }
    }

    close( fd);
    return 0;
}

int server()
{
    const int fd =3D socket( AF_UNIX, SOCK_DGRAM, 0);

    if( fd =3D=3D -1)
    {
        perror( "socket error");
        return -1;
    }

    struct sockaddr_un address{};

    strcpy( address.sun_path, path);
    address.sun_family =3D AF_UNIX;

    const int result =3D bind( fd, (struct sockaddr*)&address, sizeof =
address);

    if( result =3D=3D -1)
    {
        perror( "bind error");
        return -1;
    }

    return fd;
}

int main( int argc, char* argv[])
{
    const int fd =3D server( );

    if( fd !=3D -1)
    {
        fprintf( stdout, "%d\tnumber of packages\n", count);
        fprintf( stdout, "%d\tbytes per package\n", size);

        std::thread c{ [&](){client( );}};

        std::this_thread::sleep_for( std::chrono::microseconds( 500));
   =20
        char buffer[size] =3D {};

        for( int idx =3D 0; idx < count; ++idx)
        {
            const ssize_t result =3D recv( fd, buffer, size, 0);

            if( result =3D=3D -1)
            {
                perror("recv error");
                c.join();
                unlink( path);
                return -1;
            }

            int index =3D 0;
            memcpy( &index, buffer, sizeof idx);

            if( index !=3D idx)
            {
                fprintf( stderr, "expected %d but got %d\n", idx, =
index);
                c.join();
                unlink( path);
                return -1;
            }
        }

        c.join();
        close( fd);
        unlink( path);
    }

    return 0;
}
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