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add epoll set size tracking #1681

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egnchen Nov 9, 2025
e3ad6c7
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egnchen Nov 14, 2025
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3 changes: 3 additions & 0 deletions include/asio/detail/epoll_reactor.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -255,6 +255,9 @@ class epoll_reactor
// The interrupter is used to break a blocking epoll_wait call.
select_interrupter interrupter_;

// The epoll fd set size tracker
int epoll_fd_set_cnt_;

// The epoll file descriptor.
int epoll_fd_;

Expand Down
15 changes: 14 additions & 1 deletion include/asio/detail/impl/epoll_reactor.ipp
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Expand Up @@ -42,6 +42,7 @@ epoll_reactor::epoll_reactor(asio::execution_context& ctx)
mutex_(config(ctx).get("reactor", "registration_locking", true),
config(ctx).get("reactor", "registration_locking_spin_count", 0)),
interrupter_(config(ctx).get("reactor", "use_eventfd", true)),
epoll_fd_set_cnt(0),
epoll_fd_(do_epoll_create()),
timer_fd_(config(ctx).get("reactor", "use_timerfd", true)
? do_timerfd_create() : -1),
Expand All @@ -67,6 +68,7 @@ epoll_reactor::epoll_reactor(asio::execution_context& ctx)
ev.events = EPOLLIN | EPOLLERR;
ev.data.ptr = &timer_fd_;
epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, timer_fd_, &ev);
epoll_fd_set_cnt++;
}
}

Expand Down Expand Up @@ -108,6 +110,7 @@ void epoll_reactor::notify_fork(
::close(epoll_fd_);
epoll_fd_ = -1;
epoll_fd_ = do_epoll_create();
epoll_fd_set_cnt_ = 0;

if (timer_fd_ != -1)
{
Expand All @@ -131,6 +134,7 @@ void epoll_reactor::notify_fork(
ev.events = EPOLLIN | EPOLLERR;
ev.data.ptr = &timer_fd_;
epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, timer_fd_, &ev);
epoll_fd_set_cnt_++;
}

update_timeout();
Expand All @@ -146,6 +150,7 @@ void epoll_reactor::notify_fork(
ev.data.ptr = state;
int result = epoll_ctl(epoll_fd_,
EPOLL_CTL_ADD, state->descriptor_, &ev);
epoll_fd_set_cnt++;
if (result != 0)
{
asio::error_code ec(errno,
Expand Down Expand Up @@ -186,6 +191,7 @@ int epoll_reactor::register_descriptor(socket_type descriptor,
descriptor_data->registered_events_ = ev.events;
ev.data.ptr = descriptor_data;
int result = epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, descriptor, &ev);
epoll_fd_set_cnt_++;
if (result != 0)
{
if (errno == EPERM)
Expand Down Expand Up @@ -229,6 +235,7 @@ int epoll_reactor::register_internal_descriptor(
descriptor_data->registered_events_ = ev.events;
ev.data.ptr = descriptor_data;
int result = epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, descriptor, &ev);
epoll_fd_set_cnt_++;
if (result != 0)
{
// Don't try to re-register internal descriptor after fork().
Expand Down Expand Up @@ -419,6 +426,7 @@ void epoll_reactor::deregister_descriptor(socket_type descriptor,
epoll_event ev = { 0, { 0 } };
epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, descriptor, &ev);
}
epoll_fd_set_cnt_--;

op_queue<operation> ops;
for (int i = 0; i < max_ops; ++i)
Expand Down Expand Up @@ -465,6 +473,7 @@ void epoll_reactor::deregister_internal_descriptor(socket_type descriptor,
{
epoll_event ev = { 0, { 0 } };
epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, descriptor, &ev);
epoll_fd_set_cnt_--;

op_queue<operation> ops;
for (int i = 0; i < max_ops; ++i)
Expand Down Expand Up @@ -524,7 +533,11 @@ void epoll_reactor::run(long usec, op_queue<operation>& ops)

// Block on the epoll descriptor.
epoll_event events[128];
int num_events = epoll_wait(epoll_fd_, events, 128, timeout);
int num_events;
if (epoll_fd_set_cnt_ > 0 || timeout)
num_events = epoll_wait(epoll_fd_, events, 128, timeout);
else
num_events = 0;

#if defined(ASIO_ENABLE_HANDLER_TRACKING)
// Trace the waiting events.
Expand Down