io + socket: make pipes and sockets nonblocking by default

All normal Ruby IO methods (IO#read, IO#gets, IO#write, ...) are
all capable of appearing to be "blocking" when presented with a
file description with the O_NONBLOCK flag set; so there is
little risk of incompatibility within Ruby-using programs.

The biggest compatibility risk is when spawning external
programs.  As a result, stdin, stdout, and stderr are now always
made blocking before exec-family calls.

This change will make an event-oriented MJIT usable if it is
waiting on pipes on POSIX_like platforms.

It is ALSO necessary to take advantage of (proposed lightweight
concurrency (aka "auto-Fiber") or any similar proposal for
network concurrency: https://bugs.ruby-lang.org/issues/13618

Named-pipe (FIFO) are NOT yet non-blocking by default since
they are rarely-used and may introduce compatibility problems
and extra syscall overhead for a common path.

Please revert this commit if there are problems and if I am afk
since I am afk a lot, lately.

[ruby-core:89950] [Bug #14968]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65922 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 44 insertions, 0 deletions

diff --git a/process.c b/process.c
index 6402a425fb..241b42cd16 100644
--- a/process.c
+++ b/process.c
@@ -1474,6 +1474,39 @@ before_exec_non_async_signal_safe(void)
     rb_thread_stop_timer_thread();
 }
 
+#define WRITE_CONST(fd, str) (void)(write((fd),(str),sizeof(str)-1)<0)
+#ifdef _WIN32
+int rb_w32_set_nonblock2(int fd, int nonblock);
+#endif
+
+static int
+set_blocking(int fd)
+{
+#ifdef _WIN32
+    return rb_w32_set_nonblock2(fd, 0);
+#elif defined(F_GETFL) && defined(F_SETFL)
+    int fl = fcntl(fd, F_GETFL); /* async-signal-safe */
+
+    /* EBADF ought to be possible */
+    if (fl == -1) return fl;
+    if (fl & O_NONBLOCK) {
+        fl &= ~O_NONBLOCK;
+        return fcntl(fd, F_SETFL, fl);
+    }
+    return 0;
+#endif
+}
+
+static void
+stdfd_clear_nonblock(void)
+{
+    /* many programs cannot deal with non-blocking stdin/stdout/stderr */
+    int fd;
+    for (fd = 0; fd < 3; fd++) {
+        (void)set_blocking(fd); /* can't do much about errors anyhow */
+    }
+}
+
 static void
 before_exec(void)
 {
@@ -3445,6 +3478,11 @@ rb_execarg_run_options(const struct rb_execarg *eargp, struct rb_execarg *sargp,
             rb_execarg_allocate_dup2_tmpbuf(sargp, RARRAY_LEN(ary));
         }
     }
+    {
+        int preserve = errno;
+        stdfd_clear_nonblock();
+        errno = preserve;
+    }
 
     return 0;
 }
@@ -3645,6 +3683,12 @@ read_retry(int fd, void *buf, size_t len)
 {
     ssize_t r;
 
+    if (set_blocking(fd) != 0) {
+#ifndef _WIN32
+        rb_async_bug_errno("set_blocking failed reading child error", errno);
+#endif
+    }
+
     do {
 	r = read(fd, buf, len);
     } while (r < 0 && errno == EINTR);