Make rb_getaddrinfo interruptible

When pthread_create is available, rb_getaddrinfo creates a pthread and
executes getaddrinfo(3) in it. The caller thread waits for the pthread
to complete, but detaches it if interrupted. This allows name resolution
to be interuppted by Timeout.timeout, etc. even if it takes a long time
(for example, when the DNS server does not respond).  [Feature #19965]

ext/socket/extconf.rb

@@ -327,6 +327,8 @@ end
   net/if_dl.h
   arpa/nameser.h
   resolv.h
+  pthread.h
+  sched.h
 ].each {|h|
   if have_header(h, headers)
     headers << h
@@ -700,6 +702,11 @@ SRC
     end
   end
 
+  have_func("pthread_create")
+  have_func("pthread_detach")
+  have_func("pthread_setaffinity_np")
+  have_func("sched_getcpu")
+
   $VPATH << '$(topdir)' << '$(top_srcdir)'
   create_makefile("socket")
 end

ext/socket/raddrinfo.c

@@ -12,12 +12,17 @@
 
 // GETADDRINFO_IMPL == 0 : call getaddrinfo/getnameinfo directly
 // GETADDRINFO_IMPL == 1 : call getaddrinfo/getnameinfo without gvl (but uncancellable)
+// GETADDRINFO_IMPL == 2 : call getaddrinfo/getnameinfo in a dedicated pthread
+//                         (and if the call is interrupted, the pthread is detached)
 
 #ifndef GETADDRINFO_IMPL
 #  ifdef GETADDRINFO_EMU
 #    define GETADDRINFO_IMPL 0
-#  else
+#  elif !defined(HAVE_PTHREAD_CREATE) || !defined(HAVE_PTHREAD_DETACH)
 #    define GETADDRINFO_IMPL 1
+#  else
+#    define GETADDRINFO_IMPL 2
+#    include "ruby/thread_native.h"
 #  endif
 #endif
 
@@ -333,6 +338,183 @@ rb_getaddrinfo(const char *hostp, const char *portp, const struct addrinfo *hint
     return (int)(VALUE)rb_thread_call_without_gvl(nogvl_getaddrinfo, &arg, RUBY_UBF_IO, 0);
 }
 
+#elif GETADDRINFO_IMPL == 2
+
+struct getaddrinfo_arg
+{
+    char *node, *service;
+    struct addrinfo hints;
+    struct addrinfo *ai;
+    int err, refcount, done, cancelled;
+    rb_nativethread_lock_t lock;
+    rb_nativethread_cond_t cond;
+};
+
+static struct getaddrinfo_arg *
+allocate_getaddrinfo_arg(const char *hostp, const char *portp, const struct addrinfo *hints)
+{
+    size_t hostp_offset = sizeof(struct getaddrinfo_arg);
+    size_t portp_offset = hostp_offset + (hostp ? strlen(hostp) + 1 : 0);
+    size_t bufsize = portp_offset + (portp ? strlen(portp) + 1 : 0);
+
+    char *buf = malloc(bufsize);
+    if (!buf) {
+        rb_gc();
+        buf = malloc(bufsize);
+        if (!buf) return NULL;
+    }
+    struct getaddrinfo_arg *arg = (struct getaddrinfo_arg *)buf;
+
+    if (hostp) {
+        arg->node = buf + hostp_offset;
+        strcpy(arg->node, hostp);
+    }
+    else {
+        arg->node = NULL;
+    }
+
+    if (portp) {
+        arg->service = buf + portp_offset;
+        strcpy(arg->service, portp);
+    }
+    else {
+        arg->service = NULL;
+    }
+
+    arg->hints = *hints;
+    arg->ai = NULL;
+
+    arg->refcount = 2;
+    arg->done = arg->cancelled = 0;
+
+    rb_nativethread_lock_initialize(&arg->lock);
+    rb_native_cond_initialize(&arg->cond);
+
+    return arg;
+}
+
+static void
+free_getaddrinfo_arg(struct getaddrinfo_arg *arg)
+{
+    rb_native_cond_destroy(&arg->cond);
+    rb_nativethread_lock_destroy(&arg->lock);
+    free(arg);
+}
+
+static void *
+do_getaddrinfo(void *ptr)
+{
+    struct getaddrinfo_arg *arg = (struct getaddrinfo_arg *)ptr;
+
+    int err;
+    err = getaddrinfo(arg->node, arg->service, &arg->hints, &arg->ai);
+#ifdef __linux__
+    /* On Linux (mainly Ubuntu 13.04) /etc/nsswitch.conf has mdns4 and
+     * it cause getaddrinfo to return EAI_SYSTEM/ENOENT. [ruby-list:49420]
+     */
+    if (err == EAI_SYSTEM && errno == ENOENT)
+        err = EAI_NONAME;
+#endif
+
+    int need_free = 0;
+    rb_nativethread_lock_lock(&arg->lock);
+    arg->err = err;
+    if (arg->cancelled) {
+        freeaddrinfo(arg->ai);
+    }
+    else {
+        arg->done = 1;
+        rb_native_cond_signal(&arg->cond);
+    }
+    if (--arg->refcount == 0) need_free = 1;
+    rb_nativethread_lock_unlock(&arg->lock);
+
+    if (need_free) free_getaddrinfo_arg(arg);
+
+    return 0;
+}
+
+static void *
+wait_getaddrinfo(void *ptr)
+{
+    struct getaddrinfo_arg *arg = (struct getaddrinfo_arg *)ptr;
+    rb_nativethread_lock_lock(&arg->lock);
+    while (!arg->done && !arg->cancelled) {
+        rb_native_cond_wait(&arg->cond, &arg->lock);
+    }
+    rb_nativethread_lock_unlock(&arg->lock);
+    return 0;
+}
+
+static void
+cancel_getaddrinfo(void *ptr)
+{
+    struct getaddrinfo_arg *arg = (struct getaddrinfo_arg *)ptr;
+    rb_nativethread_lock_lock(&arg->lock);
+    arg->cancelled = 1;
+    rb_native_cond_signal(&arg->cond);
+    rb_nativethread_lock_unlock(&arg->lock);
+}
+
+static int
+rb_getaddrinfo(const char *hostp, const char *portp, const struct addrinfo *hints, struct addrinfo **ai)
+{
+    int retry;
+    struct getaddrinfo_arg *arg;
+    int err;
+
+start:
+    retry = 0;
+
+    arg = allocate_getaddrinfo_arg(hostp, portp, hints);
+    if (!arg) {
+        return ENOMEM;
+    }
+
+    pthread_t th;
+    if (pthread_create(&th, 0, do_getaddrinfo, arg) != 0) {
+        free_getaddrinfo_arg(arg);
+        return EAGAIN;
+    }
+
+    pthread_detach(th);
+#if defined(HAVE_PTHREAD_SETAFFINITY_NP) && defined(HAVE_SCHED_GETCPU)
+    cpu_set_t tmp_cpu_set;
+    CPU_ZERO(&tmp_cpu_set);
+    CPU_SET(sched_getcpu(), &tmp_cpu_set);
+    pthread_setaffinity_np(th, sizeof(cpu_set_t), &tmp_cpu_set);
+#endif
+
+    rb_thread_call_without_gvl2(wait_getaddrinfo, arg, cancel_getaddrinfo, arg);
+
+    int need_free = 0;
+    rb_nativethread_lock_lock(&arg->lock);
+    if (arg->done) {
+        err = arg->err;
+        if (err == 0) *ai = arg->ai;
+    }
+    else if (arg->cancelled) {
+        err = EAGAIN;
+    }
+    else {
+        // If already interrupted, rb_thread_call_without_gvl2 may return without calling wait_getaddrinfo.
+        // In this case, it could be !arg->done && !arg->cancelled.
+        arg->cancelled = 1; // to make do_getaddrinfo call freeaddrinfo
+        retry = 1;
+    }
+    if (--arg->refcount == 0) need_free = 1;
+    rb_nativethread_lock_unlock(&arg->lock);
+
+    if (need_free) free_getaddrinfo_arg(arg);
+
+    // If the current thread is interrupted by asynchronous exception, the following raises the exception.
+    // But if the current thread is interrupted by timer thread, the following returns; we need to manually retry.
+    rb_thread_check_ints();
+    if (retry) goto start;
+
+    return err;
+}
+
 #endif
 
 #if GETADDRINFO_IMPL == 0
@@ -345,7 +527,7 @@ rb_getnameinfo(const struct sockaddr *sa, socklen_t salen,
     return getnameinfo(sa, salen, host, hostlen, serv, servlen, flags);
 }
 
-#elif GETADDRINFO_IMPL == 1
+#elif GETADDRINFO_IMPL == 1 || GETADDRINFO_IMPL == 2 // tmp
 
 struct getnameinfo_arg
 {