Currently, opening both side of fifo in a process hangs if the
read side is opened first. The following test case exhibit the
hang while it works in linux.
#include <unistd.h>
#include <pthread.h>
#include <sys/stat.h>
#include <fcntl.h>
#define fifo1 "/tmp/fifo-test"
void *thr1(void *)
{
int fd;
usleep(100000);
fd = open(fifo1, O_WRONLY);
write(fd, "A", 1);
usleep(100000);
close(fd);
return NULL;
}
int main()
{
int fd;
pthread_t th;
char c;
mkfifo(fifo1, 0600);
pthread_create(&th, NULL, thr1, NULL);
fd = open(fifo1, O_RDONLY);
pthread_join(th, NULL);
read(fd, &c, 1);
write(1, &c, 1);
close(fd);
unlink(fifo1);
return 0;
}
The mechanism of hang is as follows. The main thread tries to open
the fifo for reading, but fhandler_fifo::open blocks until it detects
that someone is opening the fifo for writing. The other thread wants
to do that, but it never gets to the point of calling fhandler_fifo::
open because it is stuck waiting for the lock on cygheap->fdtab.
To fix this, this patch delays the construction of the cygheap_fdnew
object fd until after fhandler_fifo::open has been called.
Fixes: df63bd490a52 ("* cygheap.h (cygheap_fdmanip): New class: simplifies
locking and retrieval of fds from cygheap->fdtab.")
Reviewd-by: Ken Brown <[email protected]>
Signed-off-by: Takashi Yano <[email protected]>
---
winsup/cygwin/syscalls.cc | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index c93bf4c95..d6a2c2d3b 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -1472,11 +1472,6 @@ open (const char *unix_path, int flags, ...)
mode = va_arg (ap, mode_t);
va_end (ap);
- cygheap_fdnew fd;
-
- if (fd < 0)
- __leave; /* errno already set */
-
/* When O_PATH is specified in flags, flag bits other than O_CLOEXEC,
O_DIRECTORY, and O_NOFOLLOW are ignored. */
if (flags & O_PATH)
@@ -1577,6 +1572,12 @@ open (const char *unix_path, int flags, ...)
if ((flags & O_TMPFILE) && !fh->pc.isremote ())
try_to_bin (fh->pc, fh->get_handle (), DELETE,
FILE_OPEN_FOR_BACKUP_INTENT);
+
+ cygheap_fdnew fd;
+
+ if (fd < 0)
+ __leave; /* errno already set */
+
fd = fh;
if (fd <= 2)
set_std_handle (fd);
--
2.45.1
