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#include "ruby/ruby.h"
#include "ruby/thread.h"
#include "ruby/io.h"
#include "ruby/fiber/scheduler.h"
/*
* Test extension for reproducing the gRPC interrupt handling bug.
*
* This reproduces the exact issue from grpc/grpc commit 69f229e (June 2025):
* https://github.com/grpc/grpc/commit/69f229edd1d79ab7a7dfda98e3aef6fd807adcad
*
* The bug occurs when:
* 1. A fiber scheduler uses Thread.handle_interrupt(::SignalException => :never)
* (like Async::Scheduler does)
* 2. Native code uses rb_thread_call_without_gvl in a retry loop that checks
* the interrupted flag and retries (like gRPC's completion queue)
* 3. A signal (SIGINT/SIGTERM) is sent
* 4. The unblock_func sets interrupted=1, but Thread.handle_interrupt defers the signal
* 5. The loop sees interrupted=1 and retries without yielding to the scheduler
* 6. The deferred interrupt never gets processed -> infinite hang
*
* The fix is in vm_check_ints_blocking() in thread.c, which should yield to
* the fiber scheduler when interrupts are pending, allowing the scheduler to
* detect Thread.pending_interrupt? and exit its run loop.
*/
struct blocking_state {
int notify_descriptor;
volatile int interrupted;
};
static void
unblock_callback(void *argument)
{
struct blocking_state *blocking_state = (struct blocking_state *)argument;
blocking_state->interrupted = 1;
}
static void *
blocking_operation(void *argument)
{
struct blocking_state *blocking_state = (struct blocking_state *)argument;
ssize_t ret = write(blocking_state->notify_descriptor, "x", 1);
(void)ret; // ignore the result for now
while (!blocking_state->interrupted) {
struct timeval tv = {1, 0}; // 1 second timeout.
int result = select(0, NULL, NULL, NULL, &tv);
if (result == -1 && errno == EINTR) {
blocking_state->interrupted = 1;
}
// Otherwise, timeout -> loop again.
}
return NULL;
}
static VALUE
scheduler_blocking_loop(VALUE self, VALUE notify)
{
struct blocking_state blocking_state = {
.notify_descriptor = rb_io_descriptor(notify),
.interrupted = 0,
};
while (true) {
blocking_state.interrupted = 0;
rb_thread_call_without_gvl(
blocking_operation, &blocking_state,
unblock_callback, &blocking_state
);
// The bug: When interrupted, loop retries without yielding to scheduler.
// With Thread.handle_interrupt(:never), this causes an infinite hang,
// because the deferred interrupt never gets a chance to be processed.
} while (blocking_state.interrupted);
return Qnil;
}
void
Init_scheduler(void)
{
VALUE mBug = rb_define_module("Bug");
VALUE mScheduler = rb_define_module_under(mBug, "Scheduler");
rb_define_module_function(mScheduler, "blocking_loop", scheduler_blocking_loop, 1);
}
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