Commit 6fa6b93b authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont

Verbose comment

parent d78dcadd
...@@ -38,7 +38,6 @@ int poll (struct pollfd *fds, unsigned nfds, int timeout) ...@@ -38,7 +38,6 @@ int poll (struct pollfd *fds, unsigned nfds, int timeout)
struct timeval tv = { 0, 0 }; struct timeval tv = { 0, 0 };
int val = -1; int val = -1;
FD_ZERO (&rdset); FD_ZERO (&rdset);
FD_ZERO (&wrset); FD_ZERO (&wrset);
FD_ZERO (&exset); FD_ZERO (&exset);
...@@ -48,8 +47,26 @@ int poll (struct pollfd *fds, unsigned nfds, int timeout) ...@@ -48,8 +47,26 @@ int poll (struct pollfd *fds, unsigned nfds, int timeout)
if (val < fd) if (val < fd)
val = fd; val = fd;
/* I assume the OS has a solution select overflow if it does not have /* With POSIX, FD_SET & FD_ISSET are not defined if fd is negative or
* poll(). If it did not, we are screwed anyway. */ * bigger or equal than FD_SETSIZE. That is one of the reasons why VLC
* uses poll() rather than select(). Most POSIX systems implement
* fd_set has a bit field with no sanity checks. This is especially bad
* on systems (such as BSD) that have no process open files limit by
* default, such that it is quite feasible to get fd >= FD_SETSIZE.
* The next instructions will result in a buffer overflow if run on
* a POSIX system, and the later FD_ISSET will do undefined memory
* access.
*
* With Winsock, fd_set is a table of integers. This is awfully slow.
* However, FD_SET and FD_ISSET silently and safely discard
* overflows. If it happens we will loose socket events. Note that
* most (if not all) Winsock SOCKET handles are actually bigger than
* FD_SETSIZE in terms of absolute value - they are not POSIX file
* descriptors. From Vista, there is a much nicer WSAPoll(), but Mingw
* is yet to support it.
*
* With BeOS, the situation is unknown (FIXME: document).
*/
if (fds[i].events & POLLIN) if (fds[i].events & POLLIN)
FD_SET (fd, &rdset); FD_SET (fd, &rdset);
if (fds[i].events & POLLOUT) if (fds[i].events & POLLOUT)
......
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