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Added description of possible race condition [#CLICKHOUSE-2].

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This commit is contained in:
Alexey Milovidov 2017-09-10 06:17:05 +03:00
parent 98ad6a5db3
commit 2c424c7989
1 changed files with 17 additions and 0 deletions
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17
dbms/src/DataStreams/LazyBlockInputStream.h
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@ -60,6 +60,23 @@ protected:
{
std::lock_guard<std::mutex> lock(cancel_mutex);
/** TODO Data race here. See IProfilingBlockInputStream::collectAndSendTotalRowsApprox.
Assume following pipeline:
RemoteBlockInputStream
AsynchronousBlockInputStream
LazyBlockInputStream
RemoteBlockInputStream calls AsynchronousBlockInputStream::readPrefix
and AsynchronousBlockInputStream spawns a thread and returns.
The separate thread will call LazyBlockInputStream::read
LazyBlockInputStream::read will add more children to itself
In the same moment, in main thread, RemoteBlockInputStream::read is called,
then IProfilingBlockInputStream::collectAndSendTotalRowsApprox is called
and iterates over set of children.
*/
children.push_back(input);
if (isCancelled() && p_input)