From f29e6b3be29523e09e49e68f7dc8ed5f92586324 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=94=A1=E6=B8=A0=E6=A3=A0?= <caiqutang@kuaishang.com.cn>
Date: Mon, 11 Nov 2019 15:56:07 -0800
Subject: [PATCH] =?UTF-8?q?bugfix:=20MemTableList::RemoveOldMemTables=20in?=
 =?UTF-8?q?valid=20iterator=20after=20remov=E2=80=A6=20(#6013)?=
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Summary:
Fix issue https://github.com/facebook/rocksdb/issues/6012.

I found that it may be caused by the following codes in function _RemoveOldMemTables()_ in **db/memtable_list.cc**  :
```
  for (auto it = memlist.rbegin(); it != memlist.rend(); ++it) {
    MemTable* mem = *it;
    if (mem->GetNextLogNumber() > log_number) {
      break;
    }
    current_->Remove(mem, to_delete);
```

The iterator **it** turns invalid after `current_->Remove(mem, to_delete);`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6013

Test Plan:
```
make check
```

Differential Revision: D18401107

Pulled By: riversand963

fbshipit-source-id: bf0da3b868ed70f7aff24cf7b3e2049c0c5c7a4e
---
 db/memtable_list.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/db/memtable_list.cc b/db/memtable_list.cc
index de212b6a50..d9159b7937 100644
--- a/db/memtable_list.cc
+++ b/db/memtable_list.cc
@@ -736,17 +736,24 @@ void MemTableList::RemoveOldMemTables(uint64_t log_number,
   assert(to_delete != nullptr);
   InstallNewVersion();
   auto& memlist = current_->memlist_;
+  autovector<MemTable*> old_memtables;
   for (auto it = memlist.rbegin(); it != memlist.rend(); ++it) {
     MemTable* mem = *it;
     if (mem->GetNextLogNumber() > log_number) {
       break;
     }
+    old_memtables.push_back(mem);
+  }
+
+  for (auto it = old_memtables.begin(); it != old_memtables.end(); ++it) {
+    MemTable* mem = *it;
     current_->Remove(mem, to_delete);
     --num_flush_not_started_;
     if (0 == num_flush_not_started_) {
       imm_flush_needed.store(false, std::memory_order_release);
     }
   }
+
   UpdateMemoryUsageExcludingLast();
   ResetTrimHistoryNeeded();
 }