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Perf[BMQIO]: remove unnecessary function copy #483

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merged 2 commits into from
Nov 4, 2024
Merged

Perf[BMQIO]: remove unnecessary function copy #483

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699d567
Perf[BMQIO]: remove unnecessary function copy
678098 Oct 28, 2024
f0fcea3
Refactor[BMQIO]: get rid of setComplete
678098 Oct 30, 2024
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55 changes: 21 additions & 34 deletions src/groups/bmq/bmqio/bmqio_ntcchannel.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -406,7 +406,6 @@ NtcRead::~NtcRead()
BSLS_ASSERT_OPT(d_numNeeded == 0);
BSLS_ASSERT_OPT(d_complete);
BSLS_ASSERT_OPT(!d_timer_sp);
BSLS_ASSERT_OPT(!d_callback);
}

// MANIPULATORS
Expand All @@ -427,17 +426,6 @@ void NtcRead::setTimer(const bsl::shared_ptr<ntci::Timer>& timer)
d_timer_sp = timer;
}

void NtcRead::setComplete()
{
if (d_timer_sp) {
d_timer_sp->close();
d_timer_sp.reset();
}

d_numNeeded = 0;
d_complete = true;
}

void NtcRead::clear()
{
if (d_timer_sp) {
Expand All @@ -447,8 +435,6 @@ void NtcRead::clear()

d_numNeeded = 0;
d_complete = true;

d_callback = bmqio::Channel::ReadCallback();
}

// ACCESSORS
Expand Down Expand Up @@ -634,14 +620,12 @@ void NtcChannel::processReadTimeout(

d_readQueue.remove(read);

bool isComplete = read->isComplete();
read->setComplete();

if (d_state == e_STATE_CLOSED) {
read->clear();
return;
}

if (isComplete) {
if (read->isComplete()) {
return;
}

Expand All @@ -665,14 +649,12 @@ void NtcChannel::processReadCancelled(

d_readQueue.remove(read);

bool isComplete = read->isComplete();
read->setComplete();

if (d_state == e_STATE_CLOSED) {
read->clear();
return;
}

if (isComplete) {
if (read->isComplete()) {
return;
}

Expand Down Expand Up @@ -711,7 +693,6 @@ void NtcChannel::processReadQueueLowWatermark(
bsl::shared_ptr<bmqio::NtcRead> read = d_readQueue.front();

if (read->numNeeded() == 0 || read->isComplete()) {
read->setComplete();
read->clear();
d_readQueue.pop();
continue;
Expand Down Expand Up @@ -758,11 +739,19 @@ void NtcChannel::processReadQueueLowWatermark(

int numNeeded = 0;
{
bmqio::Channel::ReadCallback readCallback = read->callback();
const bmqio::Channel::ReadCallback& readCallback =
read->callback();

bslmt::UnLockGuard<bslmt::Mutex> unlock(&d_mutex);
readCallback(bmqio::Status(), &numNeeded, &d_readCache);
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@678098 678098 Oct 28, 2024 •
edited
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    bslmt::UnLockGuard<bslmt::Mutex> unlock(&d_mutex);
    // !!!!!!!!! `close` might be called from another thread
    readCallback(bmqio::Status(), &numNeeded, &d_readCache);

Here, we have a non-trivial thread race. In the past, we could have emptied the d_callback of NtcRead between these 2 lines of code. We make a copy of d_callback before unlocking a mutex, so we don't access the empty callback. However, it means that we can send another callback from this copy after we executed close.

My PR doesn't fix this race, so we still can send something over this callback. Instead, I make sure not to clear it from another thread, so this reference is always alive. And I also added a post-check for isComplete() to return early.

}
if (read->isComplete()) {
// It's possible that we encountered canceled or timeout event
// when we unlocked `d_mutex`, so the `read` pointer that we
// hold now might be pointing to NtcRead already removed from
// `d_readQueue`. There is nothing we can do.
continue;
}

BMQIO_NTCCHANNEL_LOG_READ_CACHE_DRAINED(this,
d_streamSocket_sp,
Expand All @@ -772,7 +761,6 @@ void NtcChannel::processReadQueueLowWatermark(
BMQIO_NTCCHANNEL_LOG_READ_COMPLETE(this,
d_streamSocket_sp,
read);
read->setComplete();
read->clear();
d_readQueue.remove(read);
continue;
Expand Down Expand Up @@ -802,10 +790,7 @@ void NtcChannel::processReadQueueLowWatermark(
bsl::shared_ptr<bmqio::NtcRead> read;
d_readQueue.pop(&read);

bool isComplete = read->isComplete();
read->setComplete();

if (!isComplete) {
if (!read->isComplete()) {
bmqio::Channel::ReadCallback readCallback = read->callback();
read->clear();

Expand Down Expand Up @@ -880,10 +865,7 @@ void NtcChannel::processShutdownReceive(
bsl::shared_ptr<bmqio::NtcRead> read;
d_readQueue.pop(&read);

bool isComplete = read->isComplete();
read->setComplete();

if (!isComplete) {
if (!read->isComplete()) {
bmqio::Channel::ReadCallback readCallback = read->callback();
read->clear();

Expand Down Expand Up @@ -1307,6 +1289,8 @@ void NtcChannel::cancelRead()

void NtcChannel::close(const Status& status)
{
// Executed from *ANY* thread

bslmt::LockGuard<bslmt::Mutex> lock(&d_mutex);

bsl::shared_ptr<NtcChannel> self = this->shared_from_this();
Expand All @@ -1319,7 +1303,10 @@ void NtcChannel::close(const Status& status)
bsl::shared_ptr<bmqio::NtcRead> read;
d_readQueue.pop(&read);

read->setComplete();
// This code assumes thread-safety of `ntci::Timer::close` because we
// are not in IO thread.
// `read->d_callback` can still be executed concurrently from IO
// thread.
read->clear();
}

Expand Down
3 changes: 0 additions & 3 deletions src/groups/bmq/bmqio/bmqio_ntcchannel.h
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Original file line number Diff line number Diff line change
Expand Up @@ -99,9 +99,6 @@ class NtcRead {
/// Set the timer to the specified `timer`.
void setTimer(const bsl::shared_ptr<ntci::Timer>& timer);

/// Set the operation as completed.
void setComplete();

/// Set the operation as completed and clear all resources.
void clear();

Expand Down
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