From 69b4671729b79d545c0b0a6ae70a3cc419f31301 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Thu, 21 Jan 2021 14:29:29 -0800
Subject: [PATCH] Use main Ractor EC on threads without EC

Previously in threads which weren't created to running Ruby (which
includes the timer thread), calling rb_postponed_job_register_one as
well as probably similar hooks would cause a segfault due to the
now-thread-local EC being NULL.

This was particularly a problem for profiling tools (like stackprof),
which rely on signal handlers, which may be sent to any thread in the
process including those not managed by Ruby.
---
 ext/-test-/postponed_job/postponed_job.c      | 27 +++++++++++++++++++
 .../-ext-/postponed_job/test_postponed_job.rb |  5 ++++
 vm_core.h                                     |  7 +++++
 3 files changed, 39 insertions(+)

diff --git a/ext/-test-/postponed_job/postponed_job.c b/ext/-test-/postponed_job/postponed_job.c
index d8684d475a45..d7d318594110 100644
--- a/ext/-test-/postponed_job/postponed_job.c
+++ b/ext/-test-/postponed_job/postponed_job.c
@@ -1,3 +1,5 @@
+#include <pthread.h>
+
 #include "ruby.h"
 #include "ruby/debug.h"
 
@@ -58,6 +60,30 @@ pjob_call_direct(VALUE self, VALUE obj)
     return self;
 }
 
+static void *
+pjob_register_in_c_thread_i(void *obj)
+{
+    rb_postponed_job_register_one(0, pjob_one_callback, (void *)obj);
+    rb_postponed_job_register_one(0, pjob_one_callback, (void *)obj);
+    rb_postponed_job_register_one(0, pjob_one_callback, (void *)obj);
+    return NULL;
+}
+
+static VALUE
+pjob_register_in_c_thread(VALUE self, VALUE obj)
+{
+	pthread_t thread;
+	if(pthread_create(&thread, NULL, pjob_register_in_c_thread_i, obj)) {
+		return Qfalse;
+	}
+
+	if(pthread_join(thread, NULL)) {
+		return Qfalse;
+	}
+
+	return Qtrue;
+}
+
 void
 Init_postponed_job(VALUE self)
 {
@@ -65,5 +91,6 @@ Init_postponed_job(VALUE self)
     rb_define_module_function(mBug, "postponed_job_register", pjob_register, 1);
     rb_define_module_function(mBug, "postponed_job_register_one", pjob_register_one, 1);
     rb_define_module_function(mBug, "postponed_job_call_direct", pjob_call_direct, 1);
+    rb_define_module_function(mBug, "postponed_job_register_in_c_thread", pjob_register_in_c_thread, 1);
 }
 
diff --git a/test/-ext-/postponed_job/test_postponed_job.rb b/test/-ext-/postponed_job/test_postponed_job.rb
index 7dc28776d0c5..22b6a02c06aa 100644
--- a/test/-ext-/postponed_job/test_postponed_job.rb
+++ b/test/-ext-/postponed_job/test_postponed_job.rb
@@ -25,4 +25,9 @@ def test_register
     Bug.postponed_job_register_one(ary = [])
     assert_equal [1], ary
   end
+
+  def test_register_in_c_thread
+    assert Bug.postponed_job_register_in_c_thread(ary = [])
+    assert_equal [1], ary
+  end
 end
diff --git a/vm_core.h b/vm_core.h
index 5f8d4ab87670..b67e5de8835e 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1788,6 +1788,8 @@ rb_ec_vm_ptr(const rb_execution_context_t *ec)
     }
 }
 
+static inline rb_vm_t * rb_current_vm(void);
+
 static inline rb_execution_context_t *
 rb_current_execution_context(void)
 {
@@ -1800,6 +1802,11 @@ rb_current_execution_context(void)
 #else
     rb_execution_context_t *ec = native_tls_get(ruby_current_ec_key);
 #endif
+
+    if (ec == NULL) {
+	    ec = rb_vm_main_ractor_ec(GET_VM());
+    }
+
     VM_ASSERT(ec != NULL);
     return ec;
 }