swebb2066 commented on PR #586:
URL: https://github.com/apache/logging-log4cxx/pull/586#issuecomment-3839357783
The following improved change also prevents a race condition when events are
added to AsyncAppender concurrently with a thread calling setBufferSize():
```
diff --git a/src/main/cpp/asyncappender.cpp b/src/main/cpp/asyncappender.cpp
index 8443d46f..a0a7c1c3 100644
--- a/src/main/cpp/asyncappender.cpp
+++ b/src/main/cpp/asyncappender.cpp
@@ -250,6 +250,11 @@ struct AsyncAppender::AsyncAppenderPriv : public
AppenderSkeleton::AppenderSkele
* Used to ensure the dispatch thread does not wait when a logging
thread is waiting.
*/
alignas(hardware_constructive_interference_size) int blockedCount{0};
+
+ /**
+ * Used to ensure resizing does not proceed when a logging thread is
adding to the buffer.
+ */
+ alignas(hardware_constructive_interference_size) std::atomic<size_t>
activeCount;
};
@@ -304,9 +309,11 @@ void AsyncAppender::doAppend(const
spi::LoggingEventPtr& event, Pool& pool1)
void AsyncAppender::append(const spi::LoggingEventPtr& event, Pool& p)
{
- if (priv->bufferSize <= 0)
+ auto activeCount = priv->activeCount.fetch_add(1,
std::memory_order_acq_rel);
+ if (priv->bufferSize <= 0 || (activeCount & 0x100000000u))
{
priv->appenders.appendLoopOnAppenders(event, p);
+ priv->activeCount.fetch_sub(1, std::memory_order_release);
return;
}
@@ -328,6 +335,7 @@ void AsyncAppender::append(const spi::LoggingEventPtr&
event, Pool& p)
priv->discardMap.emplace(loggerName, DiscardSummary{
event, LOG4CXX_STR("from an attached appender") });
else
iter->second.add(event);
+ priv->activeCount.fetch_sub(1, std::memory_order_release);
}
else while (true)
{
@@ -352,8 +360,10 @@ void AsyncAppender::append(const spi::LoggingEventPtr&
event, Pool& p)
std::this_thread::yield(); // Wait a
bit
}
priv->bufferNotEmpty.notify_all();
+ priv->activeCount.fetch_sub(1,
std::memory_order_release);
break;
}
+ priv->activeCount.fetch_sub(1, std::memory_order_release);
//
// Following code is only reachable if buffer is full or
eventCount has overflowed
//
@@ -397,6 +407,7 @@ void AsyncAppender::append(const spi::LoggingEventPtr&
event, Pool& p)
break;
}
+ priv->activeCount.fetch_add(1, std::memory_order_acq_rel);
}
}
@@ -472,9 +483,17 @@ void AsyncAppender::setBufferSize(int size)
throw IllegalArgumentException(LOG4CXX_STR("size argument
must be non-negative"));
}
+ auto activeCount = priv->activeCount.fetch_add(0x100000000u,
std::memory_order_acq_rel) & 0xFFFFFFFFu;
+ while (activeCount || priv->commitCount != priv->dispatchedCount)
+ {
+ priv->bufferNotEmpty.notify_all();
+ std::this_thread::yield(); // Wait a bit
+ activeCount = priv->activeCount & 0xFFFFFFFFu;
+ }
std::lock_guard<std::mutex> lock(priv->bufferMutex);
priv->bufferSize = (size < 1) ? 1 : size;
priv->buffer.resize(priv->bufferSize);
+ priv->activeCount.fetch_sub(0x100000000u, std::memory_order_release);
priv->bufferNotFull.notify_all();
}
```
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