Weird behavior with writes to a unix socket pair
Hi,
I've been testing the effects of the SO_RCVBUF/SO_SNDBUF socket options
on unix sockets on various platforms, and I've run into some curious
unix socket behavior on Cygwin (independent of the SO_RCVBUF/SO_SNDBUF
options).
This piece of code should get blocked in one of the writes (and it does
so for regular pipes):
#include
#include
#include
int main()
{
int p[2];
socketpair(AF_LOCAL, SOCK_STREAM, 0,p);
/*pipe(p);*/
/*setsockopt(p[0], SOL_SOCKET, SO_RCVBUF, &(int){1},sizeof(int));*/
/*setsockopt(p[0], SOL_SOCKET, SO_SNDBUF, &(int){1},sizeof(int));*/
/*setsockopt(p[1], SOL_SOCKET, SO_RCVBUF, &(int){1},sizeof(int));*/
/*setsockopt(p[1], SOL_SOCKET, SO_SNDBUF, &(int){1},sizeof(int));*/
ssize_t n;
for(unsigned j=0;j<1;j++)
for(unsigned char i=1; i!=0; i++){
printf("%u\n", j*256+i);
if(0>(n=write(p[1],,1))) perror("write");
}
}
but with a unix socket socket pair a first couple of writes proceed
quickly and then the writes continue to proceed with ever-increasing
intervals between them.
I don't see why it should behave like this and I think you guys might
want to look into why it does.
Best regards,
Petr Skocik
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malloc(0) crashing with SIGABRT
There's been a twitter discussion on how different POSIX platforms handle malloc(0): https://twitter.com/sortiecat/status/1170697927804817412 . As for Cygwin, the answer appears to be "not well", but this should be easy to fix. Best regards, Petr Skocik -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
malloc(0) crashes with SIGABRT
https://twitter.com/sortiecat/status/1170697927804817412 -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
bind() behavior inconsistency with Linux and MacOS
Hi.
I don't know if this is technically a bug, but I've noticed that unlike
on Linux or MacOS, I a cannot bind a unix domain socket in a child
process and then listen on it in the parent.
The bind succeeds but `listen()` in the parent then fails with EINVAL.
(The reason I'd like to `bind` in a different process is so I could
`chdir` to a different directory before `bind`ing and then conceptually
back without having the `chdir` break file operations in different threads.)
Just wanted to let you guys know in case there was an easy fix.
Best regards,
Petr Skocik
Example code:
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
int main(int C, char **V)
{
int sfd; if(0>(sfd=socket(AF_UNIX, SOCK_STREAM, 0),1)) return
perror("socket"),1;
struct sockaddr_un uaddr; uaddr.sun_family = AF_UNIX;
char const *nm = "FOO.sock"; size_t nmlen =
nm[0]?strlen(nm):(1+strlen([1]));
size_t actlen = nmlen <= sizeof(uaddr.sun_path)-1 ? nmlen :
sizeof(uaddr.sun_path)-1;
memcpy(_path[0],nm,actlen);
uaddr.sun_path[actlen]='\0';
size_t socklen = 0 ? sizeof(struct sockaddr_un) : offsetof(struct
sockaddr_un, sun_path) + actlen + 1;
fflush(stdout);
pid_t pid=0;
int fork_eh = atoi(V[1]?V[1]:"1");
if(fork_eh)
if(0>(pid=fork())) return perror("fork"),1;
if(0==pid){
printf("pid=%d binding\n", (int)getpid());
if(0>bind(sfd, (struct sockaddr*), (socklen_t)+socklen))
perror("bind"),_exit(1);
printf("pid=%d bound\n", (int)getpid());
fflush(stdout);
if(fork_eh) _exit(0);
}
wait(0);
if(0>listen(sfd,INT_MAX)) return perror("listen"),1;
printf("pid=%d listening\n", (int)getpid());
}
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Re: uc_sigmask set in a sigaction signal handler not honored
> On Apr 3 14:15, Corinna Vinschen wrote:
> > On Apr 3 11:27, Petr Skočík wrote:
> > > Hi. Correct me if I'm wrong but POSIX appears to define
> > >
> > > https://pubs.opengroup.org/onlinepubs/7908799/xsh/ucontext.h.html
> > >
> > > as, among other things, containing the field:
> > >
> > > sigset_tuc_sigmask the set of signals that are blocked when this
> > > context is active
> > >
> > > and it also specifies that the third argument to a .sa_sigaction
> > > signal handler is a ucontext_t* cast to void*.
> > >
> > > So it should follow that doing
> > >
> > > void act(int Sig, siginfo_t *Info, void *Uctx)
> > > {
> > > ucontext_t *uctx = Uctx;
> > > sigfillset(>uc_sigmask);
> > > }
> > >
> > > from a signal handler should alter the signal mask of the thread the
> > > signal ran on.
> > >
> > > This is how Linux and MacOS behave, but not CygWin, as the following
> > > program shows:
> >
> > What you're asking for is really complicated.
> >
> > The context given to act is the context at the time the signal function
> > is called. In Cygwin (lower case w) this is a copy of the context.
> >
> > sigfillset() has not the faintest clue where this context comes from, it
> > just sets the signal mask value without taking any further action.
> >
> > There are no provisions to control if the called function changes the
> > context, other than via setcontext / swapcontext, and I don't see that
> > POSIX requires anything else. Both functions change the current
> > thread's sigmask according to the value of uc_sigmask.
>
> Or maybe I'm just dumb. Would it suffice if the thread's signal mask is
> changed to uc_sigmask when the signal function returns?
>
>
> Corinna
Thanks for the feedback.
> Would it suffice if the thread's signal mask is
> changed to uc_sigmask when the signal function returns?
That is the idea. It's what Linux and MacOS do.
Petr Skocik
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uc_sigmask set in a sigaction signal handler not honored
Hi. Correct me if I'm wrong but POSIX appears to define
https://pubs.opengroup.org/onlinepubs/7908799/xsh/ucontext.h.html
as, among other things, containing the field:
sigset_tuc_sigmask the set of signals that are blocked when this
context is active
and it also specifies that the third argument to a .sa_sigaction
signal handler is a ucontext_t* cast to void*.
So it should follow that doing
void act(int Sig, siginfo_t *Info, void *Uctx)
{
ucontext_t *uctx = Uctx;
sigfillset(>uc_sigmask);
}
from a signal handler should alter the signal mask of the thread the
signal ran on.
This is how Linux and MacOS behave, but not CygWin, as the following
program shows:
#include
#include
#include
#include
#include
void prmask(void)
{
sigset_t mask; pthread_sigmask(SIG_SETMASK,0,);
for(int i=1; i<=64; i++){ printf("%d", sigismember(,i)); }
puts("");
}
void act(int Sig, siginfo_t *Info, void *Uctx)
{
ucontext_t *uctx = Uctx;
sigfillset(>uc_sigmask);
}
int main()
{
struct sigaction sa;
sa.sa_sigaction = act;
sa.sa_flags = SA_SIGINFO;
sigfillset(_mask);
prmask();
sigaction(SIGINT,,0);
sigaction(SIGALRM,,0);
if(1)
setitimer(ITIMER_REAL,&(struct
itimerval){.it_value={.tv_usec=1}},0);
pause();
prmask();
}
I think this is a bug, so I'm reporting it. Do you think it can be fixed
in the near future?
Best regards,
Petr Skocik
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