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// Licensed to the Apache Software Foundation (ASF) under one
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// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
#pragma once
#include <memory>
#include <unordered_map>
#include <vector>
#include <boost/thread/shared_mutex.hpp>
namespace impala {
class MemTracker;
class ScanNode;
/// Class to keep track of scanner threads for a query on the current backend.
/// Tracks the number of threads and their expected memory consumption
/// for the purpose of limiting the aggregate memory consumption of scanner threads.
/// This allows us to implement some heuristics that help prevent us going over the
/// query memory limit by creating too many scanner threads.
/// TODO: this can be removed once all scan nodes are switched to the MT versions.
class ScannerMemLimiter {
/// Register a scan and track the estimated memory 'estimated_initial_thread_mem'
/// for the initial threads. 'node' must live as long as this object is in use
/// (i.e. as long as the below methods are being called). Each 'node' can only
/// be registered once.
void RegisterScan(ScanNode* node, int64_t estimated_initial_thread_mem);
/// Returns true if there is enough memory available to create a scanner thread
/// for node 'node_id' that is estimated to consume 'estimated_thread_mem' bytes
/// of memory. Updates the state of the limiter to reflect the increased memory.
/// The caller must call ReleaseMemoryForScannerThread() for every successful
/// call to this function.
bool ClaimMemoryForScannerThread(ScanNode* node, int64_t estimated_thread_mem);
/// Must be called when a scanner thread exits. Releases the memory accounted for
/// by ClaimMemoryForScannerThread().
void ReleaseMemoryForScannerThread(ScanNode* node, int64_t estimated_thread_mem);
struct RegisteredScan;
/// Protects below data structures.
boost::shared_mutex registered_scans_lock_;
/// All of this query's scan nodes. The scan nodes register themselves in their
/// Prepare() phase. Threads must hold 'registered_scans_lock_' in shared mode
/// when reading or in exclusive mode when modifying. The total memory currently
/// consumed by the scans is calculated by iterating over this map, which is
/// O(n) in the number of scans. With an unlimited number of thread tokens,
/// this would mean we do O(n^2) work per query, but in practice if there are a large
/// number of concurrent scans there will be no available thread tokens and
/// ClaimMemoryForScannerThread() will not be called.
std::unordered_map<ScanNode*, std::unique_ptr<RegisteredScan>> registered_scans_;