1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
|
#pragma once
#include <IO/BufferWithOwnMemory.h>
#include <IO/ReadBuffer.h>
#include <IO/SeekableReadBuffer.h>
#include <Interpreters/threadPoolCallbackRunner.h>
#include <Common/ArenaWithFreeLists.h>
namespace DB
{
/**
* Reads from multiple positions in a ReadBuffer in parallel.
* Then reassembles the data into one stream in the original order.
*
* Each working reader reads its segment of data into a buffer.
*
* ParallelReadBuffer in nextImpl method take first available segment from first reader in deque and reports it it to user.
* When first reader finishes reading, they will be removed from worker deque and data from next reader consumed.
*
* Number of working readers limited by max_working_readers.
*/
class ParallelReadBuffer : public SeekableReadBuffer, public WithFileSize
{
private:
/// Blocks until data occurred in the first reader or this reader indicate finishing
/// Finished readers removed from queue and data from next readers processed
bool nextImpl() override;
public:
ParallelReadBuffer(SeekableReadBuffer & input, ThreadPoolCallbackRunner<void> schedule_, size_t max_working_readers, size_t range_step_, size_t file_size);
~ParallelReadBuffer() override { finishAndWait(); }
off_t seek(off_t off, int whence) override;
size_t getFileSize() override;
off_t getPosition() override;
const SeekableReadBuffer & getReadBuffer() const { return input; }
SeekableReadBuffer & getReadBuffer() { return input; }
private:
/// Reader in progress with a buffer for the segment
struct ReadWorker;
using ReadWorkerPtr = std::shared_ptr<ReadWorker>;
/// First worker in deque have new data or processed all available amount
bool currentWorkerReady() const;
/// First worker in deque processed and flushed all data
bool currentWorkerCompleted() const;
[[noreturn]] void handleEmergencyStop();
void addReaders();
bool addReaderToPool();
/// Process read_worker, read data and save into the buffer
void readerThreadFunction(ReadWorkerPtr read_worker);
void onBackgroundException();
void finishAndWait();
size_t max_working_readers;
std::atomic_size_t active_working_readers{0};
ThreadPoolCallbackRunner<void> schedule;
SeekableReadBuffer & input;
size_t file_size;
size_t range_step;
size_t next_range_start{0};
/**
* FIFO queue of readers.
* Each worker contains a buffer for the downloaded segment.
* After all data for the segment is read and delivered to the user, the reader will be removed
* from deque and data from next reader will be delivered.
* After removing from deque, call addReaders().
*/
std::deque<ReadWorkerPtr> read_workers;
/// Triggered when new data available
std::condition_variable next_condvar;
std::mutex exception_mutex;
std::exception_ptr background_exception = nullptr;
std::atomic_bool emergency_stop{false};
off_t current_position{0}; // end of working_buffer
bool all_completed{false};
};
/// If `buf` is a SeekableReadBuffer with supportsReadAt() == true, creates a ParallelReadBuffer
/// from it. Otherwise returns nullptr;
std::unique_ptr<ParallelReadBuffer> wrapInParallelReadBufferIfSupported(
ReadBuffer & buf, ThreadPoolCallbackRunner<void> schedule, size_t max_working_readers,
size_t range_step, size_t file_size);
}
|
