thread.c (call_without_gvl): spawn thread for UBF iff single-threaded

We need another native thread to call some unblocking functions
which aren't RUBY_UBF_IO or RUBY_UBF_PROCESS.  Instead of a
permanent thread in <= 2.5, we can now rely on the thread cache
feature to perform interrupts.

[ruby-core:90865] [Bug #15499]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66708 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 19 insertions, 0 deletions

diff --git a/thread_pthread.c b/thread_pthread.c
index e074a854f5..d8d3184c62 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -2206,4 +2206,23 @@ timer_pthread_fn(void *p)
     return 0;
 }
 #endif /* UBF_TIMER_PTHREAD */
+
+static VALUE
+ubf_caller(const void *ignore)
+{
+    rb_thread_sleep_forever();
+
+    return Qfalse;
+}
+
+/*
+ * Called if and only if one thread is running, and
+ * the unblock function is NOT async-signal-safe
+ * This assumes USE_THREAD_CACHE is true for performance reasons
+ */
+static VALUE
+rb_thread_start_unblock_thread(void)
+{
+    return rb_thread_create(ubf_caller, 0);
+}
 #endif /* THREAD_SYSTEM_DEPENDENT_IMPLEMENTATION */