Fix assertion failure in FIFO compaction with TTL (#5754)

Summary:
Before this PR, the following sequence of events can cause assertion failure as shown below.
Stack trace (partial):
```
(gdb) bt
2  0x00007f59b350ad15 in __assert_fail_base (fmt=<optimized out>, assertion=assertion@entry=0x9f8390 "mark_as_compacted ? !inputs_[i][j]->being_compacted : inputs_[i][j]->being_compacted", file=file@entry=0x9e347c "db/compaction/compaction.cc", line=line@entry=395, function=function@entry=0xa21ec0 <rocksdb::Compaction::MarkFilesBeingCompacted(bool)::__PRETTY_FUNCTION__> "void rocksdb::Compaction::MarkFilesBeingCompacted(bool)") at assert.c:92
3  0x00007f59b350adc3 in __GI___assert_fail (assertion=assertion@entry=0x9f8390 "mark_as_compacted ? !inputs_[i][j]->being_compacted : inputs_[i][j]->being_compacted", file=file@entry=0x9e347c "db/compaction/compaction.cc", line=line@entry=395, function=function@entry=0xa21ec0 <rocksdb::Compaction::MarkFilesBeingCompacted(bool)::__PRETTY_FUNCTION__> "void rocksdb::Compaction::MarkFilesBeingCompacted(bool)") at assert.c:101
4  0x0000000000492ccd in rocksdb::Compaction::MarkFilesBeingCompacted (this=<optimized out>, mark_as_compacted=<optimized out>) at db/compaction/compaction.cc:394
5  0x000000000049467a in rocksdb::Compaction::Compaction (this=0x7f59af013000, vstorage=0x7f581af53030, _immutable_cf_options=..., _mutable_cf_options=..., _inputs=..., _output_level=<optimized out>, _target_file_size=0, _max_compaction_bytes=0, _output_path_id=0, _compression=<incomplete type>, _compression_opts=..., _max_subcompactions=0, _grandparents=..., _manual_compaction=false, _score=4, _deletion_compaction=true, _compaction_reason=rocksdb::CompactionReason::kFIFOTtl) at db/compaction/compaction.cc:241
6  0x00000000004af9bc in rocksdb::FIFOCompactionPicker::PickTTLCompaction (this=0x7f59b31a6900, cf_name=..., mutable_cf_options=..., vstorage=0x7f581af53030, log_buffer=log_buffer@entry=0x7f59b1bfa930) at db/compaction/compaction_picker_fifo.cc:101
7  0x00000000004b0771 in rocksdb::FIFOCompactionPicker::PickCompaction (this=0x7f59b31a6900, cf_name=..., mutable_cf_options=..., vstorage=0x7f581af53030, log_buffer=0x7f59b1bfa930) at db/compaction/compaction_picker_fifo.cc:201
8  0x00000000004838cc in rocksdb::ColumnFamilyData::PickCompaction (this=this@entry=0x7f59b31b3700, mutable_options=..., log_buffer=log_buffer@entry=0x7f59b1bfa930) at db/column_family.cc:933
9  0x00000000004f3645 in rocksdb::DBImpl::BackgroundCompaction (this=this@entry=0x7f59b3176000, made_progress=made_progress@entry=0x7f59b1bfa6bf, job_context=job_context@entry=0x7f59b1bfa760, log_buffer=log_buffer@entry=0x7f59b1bfa930, prepicked_compaction=prepicked_compaction@entry=0x0, thread_pri=rocksdb::Env::LOW) at db/db_impl/db_impl_compaction_flush.cc:2541
10 0x00000000004f5e2a in rocksdb::DBImpl::BackgroundCallCompaction (this=this@entry=0x7f59b3176000, prepicked_compaction=prepicked_compaction@entry=0x0, bg_thread_pri=bg_thread_pri@entry=rocksdb::Env::LOW) at db/db_impl/db_impl_compaction_flush.cc:2312
11 0x00000000004f648e in rocksdb::DBImpl::BGWorkCompaction (arg=<optimized out>) at db/db_impl/db_impl_compaction_flush.cc:2087
```
This can be caused by the following sequence of events.
```
Time
|      thr          bg_compact_thr1                     bg_compact_thr2
|      write
|      flush
|                   mark all l0 as being compacted
|      write
|      flush
|                   add cf to queue again
|                                                       mark all l0 as being
|                                                       compacted, fail the
|                                                       assertion
V
```
Test plan (on devserver)
Since bg_compact_thr1 and bg_compact_thr2 are two threads executing the same
code, it is difficult to use sync point dependency to
coordinate their execution. Therefore, I choose to use db_stress.
```
$TEST_TMPDIR=/dev/shm/rocksdb ./db_stress --periodic_compaction_seconds=1 --max_background_compactions=20 --format_version=2 --memtablerep=skip_list --max_write_buffer_number=3 --cache_index_and_filter_blocks=1 --reopen=20 --recycle_log_file_num=0 --acquire_snapshot_one_in=10000 --delpercent=4 --log2_keys_per_lock=22 --compaction_ttl=1 --block_size=16384 --use_multiget=1 --compact_files_one_in=1000000 --target_file_size_multiplier=2 --clear_column_family_one_in=0 --max_bytes_for_level_base=10485760 --use_full_merge_v1=1 --target_file_size_base=2097152 --checkpoint_one_in=1000000 --mmap_read=0 --compression_type=zstd --writepercent=35 --readpercent=45 --subcompactions=4 --use_merge=0 --write_buffer_size=4194304 --test_batches_snapshots=0 --db=/dev/shm/rocksdb/rocksdb_crashtest_whitebox --use_direct_reads=0 --compact_range_one_in=1000000 --open_files=-1 --destroy_db_initially=0 --progress_reports=0 --compression_zstd_max_train_bytes=0 --snapshot_hold_ops=100000 --enable_pipelined_write=0 --nooverwritepercent=1 --compression_max_dict_bytes=0 --max_key=1000000 --prefixpercent=5 --flush_one_in=1000000 --ops_per_thread=40000 --index_block_restart_interval=7 --cache_size=1048576 --compaction_style=2 --verify_checksum=1 --delrangepercent=1 --use_direct_io_for_flush_and_compaction=0
```
This should see no assertion failure.
Last but not least,
```
$COMPILE_WITH_ASAN=1 make -j32 all
$make check
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5754

Differential Revision: D17109791

Pulled By: riversand963

fbshipit-source-id: 25fc46101235add158554e096540b72c324be078

db/compaction/compaction_picker_fifo.cc

@@ -54,6 +54,15 @@ Compaction* FIFOCompactionPicker::PickTTLCompaction(
   }
   const uint64_t current_time = static_cast<uint64_t>(_current_time);
 
+  if (!level0_compactions_in_progress_.empty()) {
+    ROCKS_LOG_BUFFER(
+        log_buffer,
+        "[%s] FIFO compaction: Already executing compaction. No need "
+        "to run parallel compactions since compactions are very fast",
+        cf_name.c_str());
+    return nullptr;
+  }
+
   std::vector<CompactionInputFiles> inputs;
   inputs.emplace_back();
   inputs[0].level = 0;