[opt](MultiCast) Avoid copying while holding a lock

be/src/pipeline/exec/multi_cast_data_streamer.cpp

@@ -21,31 +21,41 @@
 
 namespace doris::pipeline {
 
-MultiCastBlock::MultiCastBlock(vectorized::Block* block, int used_count, size_t mem_size)
-        : _used_count(used_count), _mem_size(mem_size) {
+MultiCastBlock::MultiCastBlock(vectorized::Block* block, int used_count, int un_finish_copy,
+                               size_t mem_size)
+        : _used_count(used_count), _un_finish_copy(un_finish_copy), _mem_size(mem_size) {
     _block = vectorized::Block::create_unique(block->get_columns_with_type_and_name());
     block->clear();
 }
 
 Status MultiCastDataStreamer::pull(int sender_idx, doris::vectorized::Block* block, bool* eos) {
-    std::lock_guard l(_mutex);
-    auto& pos_to_pull = _sender_pos_to_read[sender_idx];
-    if (pos_to_pull != _multi_cast_blocks.end()) {
-        if (pos_to_pull->_used_count == 1) {
-            DCHECK(pos_to_pull == _multi_cast_blocks.begin());
-            pos_to_pull->_block->swap(*block);
+    int* un_finish_copy = nullptr;
+    int use_count = 0;
+    {
+        std::lock_guard l(_mutex);
+        auto& pos_to_pull = _sender_pos_to_read[sender_idx];
+        const auto end = _multi_cast_blocks.end();
+        if (pos_to_pull != end) {
+            *block = *pos_to_pull->_block;
 
             _cumulative_mem_size -= pos_to_pull->_mem_size;
-            pos_to_pull++;
-            _multi_cast_blocks.pop_front();
-        } else {
-            pos_to_pull->_block->create_same_struct_block(0)->swap(*block);
-            RETURN_IF_ERROR(vectorized::MutableBlock(block).merge(*pos_to_pull->_block));
             pos_to_pull->_used_count--;
+            use_count = pos_to_pull->_used_count;
+            un_finish_copy = &pos_to_pull->_un_finish_copy;
+
             pos_to_pull++;
         }
+        *eos = _eos and pos_to_pull == end;
+    }
+
+    if (un_finish_copy) {
+        if (use_count == 0) {
+            // will clear _multi_cast_blocks
+            _wait_copy_block(block, *un_finish_copy);
+        } else {
+            _copy_block(block, *un_finish_copy);
+        }
     }
-    *eos = _eos and pos_to_pull == _multi_cast_blocks.end();
     return Status::OK();
 }
 
@@ -60,12 +70,33 @@ void MultiCastDataStreamer::close_sender(int sender_idx) {
             _multi_cast_blocks.pop_front();
         } else {
             pos_to_pull->_used_count--;
+            pos_to_pull->_un_finish_copy--;
             pos_to_pull++;
         }
     }
     _closed_sender_count++;
 }
 
+void MultiCastDataStreamer::_copy_block(vectorized::Block* block, int& un_finish_copy) {
+    const auto rows = block->rows();
+    for (int i = 0; i < block->columns(); ++i) {
+        block->get_by_position(i).column = block->get_by_position(i).column->clone_resized(rows);
+    }
+
+    std::unique_lock l(_mutex);
+    un_finish_copy--;
+    if (un_finish_copy == 0) {
+        l.unlock();
+        _cv.notify_one();
+    }
+}
+
+void MultiCastDataStreamer::_wait_copy_block(vectorized::Block* block, int& un_finish_copy) {
+    std::unique_lock l(_mutex);
+    _cv.wait(l, [&]() { return un_finish_copy == 0; });
+    _multi_cast_blocks.pop_front();
+}
+
 Status MultiCastDataStreamer::push(RuntimeState* state, doris::vectorized::Block* block, bool eos) {
     auto rows = block->rows();
     COUNTER_UPDATE(_process_rows, rows);
@@ -79,7 +110,8 @@ Status MultiCastDataStreamer::push(RuntimeState* state, doris::vectorized::Block
     // TODO: if the [queue back block rows + block->rows()] < batch_size, better
     // do merge block. but need check the need_process_count and used_count whether
     // equal
-    _multi_cast_blocks.emplace_back(block, need_process_count, block_mem_size);
+    _multi_cast_blocks.emplace_back(block, need_process_count, need_process_count - 1,
+                                    block_mem_size);
     _cumulative_mem_size += block_mem_size;
     COUNTER_SET(_peak_mem_usage, std::max(_cumulative_mem_size, _peak_mem_usage->value()));
 

be/src/pipeline/exec/multi_cast_data_streamer.h

@@ -22,10 +22,11 @@
 namespace doris::pipeline {
 
 struct MultiCastBlock {
-    MultiCastBlock(vectorized::Block* block, int used_count, size_t mem_size);
+    MultiCastBlock(vectorized::Block* block, int used_count, int need_copy, size_t mem_size);
 
     std::unique_ptr<vectorized::Block> _block;
     int _used_count;
+    int _un_finish_copy;
     size_t _mem_size;
 };
 
@@ -68,6 +69,12 @@ class MultiCastDataStreamer {
     }
 
 private:
+    void _copy_block(vectorized::Block* block, int& un_finish_copy);
+
+    void _wait_copy_block(vectorized::Block* block, int& un_finish_copy);
+
+    std::condition_variable _cv;
+
     const RowDescriptor& _row_desc;
     RuntimeProfile* _profile;
     std::list<MultiCastBlock> _multi_cast_blocks;