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[4.0] Fix possible segfault switching between read/write windows #1719

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merged 4 commits into from
Oct 6, 2023
Merged

[4.0] Fix possible segfault switching between read/write windows #1719

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6af28bb
GH-1639 Fix producer_plugin shutdown of read only threads to prevent …
heifner Sep 18, 2023
3854555
GH-1716 pop before execute as the executed lambda can switch to read-…
heifner Oct 4, 2023
c94682f
Fix merge issue
heifner Oct 4, 2023
adc24ae
Reuse same ec
heifner Oct 5, 2023
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5 changes: 5 additions & 0 deletions libraries/custom_appbase/include/eosio/chain/application.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,11 @@ class two_queue_executor {
else
return read_only_queue_.wrap( priority, --order_, std::forward<Function>( func));
}

void stop() {
read_only_queue_.stop();
read_write_queue_.stop();
}

void clear() {
read_only_queue_.clear();
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30 changes: 19 additions & 11 deletions libraries/custom_appbase/include/eosio/chain/exec_pri_queue.hpp
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Expand Up @@ -13,6 +13,12 @@ class exec_pri_queue : public boost::asio::execution_context
{
public:

void stop() {
std::lock_guard g( mtx_ );
exiting_blocking_ = true;
cond_.notify_all();
}

void enable_locking(uint32_t num_threads, std::function<bool()> should_exit) {
assert(num_threads > 0 && num_waiting_ == 0);
lock_enabled_ = true;
Expand Down Expand Up @@ -47,17 +53,6 @@ class exec_pri_queue : public boost::asio::execution_context
handlers_ = prio_queue();
}

// only call when no lock required
bool execute_highest()
{
if( !handlers_.empty() ) {
handlers_.top()->execute();
handlers_.pop();
}

return !handlers_.empty();
}

private:
// has to be defined before use, auto return type
auto pop() {
Expand All @@ -68,6 +63,19 @@ class exec_pri_queue : public boost::asio::execution_context

public:

// only call when no lock required
bool execute_highest()
{
if( !handlers_.empty() ) {
auto t = pop();
bool empty = handlers_.empty();
t->execute();
return !empty;
}

return false;
}
Comment on lines +67 to +77
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No need to change, but just to chat I would have written it like that.

Suggested change
bool execute_highest()
{
if( !handlers_.empty() ) {
auto t = pop();
bool empty = handlers_.empty();
t->execute();
return !empty;
}
return false;
}
bool execute_highest()
{
bool empty = handlers_.empty();
if( !empty ) {
auto t = pop();
empty = handlers_.empty();
t->execute();
}
return !empty;
}


bool execute_highest_locked(bool should_block) {
std::unique_lock g(mtx_);
if (should_block) {
Expand Down
4 changes: 2 additions & 2 deletions libraries/custom_appbase/tests/custom_appbase_tests.cpp
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Expand Up @@ -40,7 +40,7 @@ BOOST_AUTO_TEST_CASE( default_exec_window ) {
app->executor().post( priority::lowest, exec_queue::read_only, [&]() {
// read_only_queue should only contain the current lambda function,
// and read_write_queue should have executed all its functions
BOOST_REQUIRE_EQUAL( app->executor().read_only_queue().size(), 1); // pop()s after execute
BOOST_REQUIRE_EQUAL( app->executor().read_only_queue().size(), 0); // pop()s before execute
BOOST_REQUIRE_EQUAL( app->executor().read_write_queue().size(), 0 );
app->quit();
} );
Expand Down Expand Up @@ -175,7 +175,7 @@ BOOST_AUTO_TEST_CASE( execute_from_both_queues ) {
// stop application. Use lowest at the end to make sure this executes the last
app->executor().post( priority::lowest, exec_queue::read_only, [&]() {
// read_queue should have current function and write_queue's functions are all executed
BOOST_REQUIRE_EQUAL( app->executor().read_only_queue().size(), 1); // pop()s after execute
BOOST_REQUIRE_EQUAL( app->executor().read_only_queue().size(), 0); // pop()s before execute
BOOST_REQUIRE_EQUAL( app->executor().read_write_queue().size(), 0 );
app->quit();
} );
Expand Down
19 changes: 6 additions & 13 deletions plugins/producer_plugin/producer_plugin.cpp
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Expand Up @@ -1389,20 +1389,13 @@ void producer_plugin::plugin_startup()
} FC_CAPTURE_AND_RETHROW() }

void producer_plugin::plugin_shutdown() {
try {
my->_timer.cancel();
} catch ( const std::bad_alloc& ) {
chain_plugin::handle_bad_alloc();
} catch ( const boost::interprocess::bad_alloc& ) {
chain_plugin::handle_bad_alloc();
} catch(const fc::exception& e) {
edump((e.to_detail_string()));
} catch(const std::exception& e) {
edump((fc::std_exception_wrapper::from_current_exception(e).to_detail_string()));
}

boost::system::error_code ec;
my->_timer.cancel(ec);
boost::system::error_code ro_ec;
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there doesn't appear to be a need for the second ro_ec here

my->_ro_timer.cancel(ro_ec);
app().executor().stop();
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Can you explain this line some more? In what cases would we make it here and the appbase executor would still be running?

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The appbase executor is not running here. However, the read-only threads can still be running and some can be paused on the condition variable in exec_pri_queue, trying to then join their threads cause them to deadlock.

my->_ro_thread_pool.stop();
my->_thread_pool.stop();

my->_unapplied_transactions.clear();

app().executor().post( 0, [me = my](){} ); // keep my pointer alive until queue is drained
Expand Down