From e3d97d5f8ebfdd07831d4f5002648fb285999a67 Mon Sep 17 00:00:00 2001
From: Rafael Kitover <rkitover@gmail.com>
Date: Sat, 24 Aug 2019 01:02:38 +0000
Subject: [PATCH] limit max thread count to 126

When the number of threads is higher than 126 the number of LMDB locks
is exhausted and `ArmoryDB` dies with the error:

```
MDB_READERS_FULL: Environment maxreaders limit reached
```

See:
https://github.com/lmdbjava/lmdbjava/issues/65#issuecomment-322761020

Replace the uses of `std::thread::hardware_concurrency()` with a new
function `MAX_THREADS()` which limits the number of threads to `126`.

This is a temporary fix, the real fix would be making sure the number of
LMDB locks is sufficient.

However, a configured value for the maximum number of threads would also
be useful.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>
---
 cppForSwig/BDM_Server.cpp             |  2 +-
 cppForSwig/BlockDataManagerConfig.cpp | 14 ++++++++++++++
 cppForSwig/BlockDataManagerConfig.h   |  4 +++-
 cppForSwig/Server.cpp                 |  4 ++--
 cppForSwig/ZeroConf.cpp               |  4 ++--
 5 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/cppForSwig/BDM_Server.cpp b/cppForSwig/BDM_Server.cpp
index 025f0b8f4..9489467bc 100644
--- a/cppForSwig/BDM_Server.cpp
+++ b/cppForSwig/BDM_Server.cpp
@@ -1848,7 +1848,7 @@ void Clients::init(BlockDataManagerThread* bdmT,
    unsigned innerThreadCount = 2;
    if (BlockDataManagerConfig::getDbType() == ARMORY_DB_SUPER &&
       BlockDataManagerConfig::getOperationMode() != OPERATION_UNITTEST)
-      innerThreadCount = thread::hardware_concurrency();
+      innerThreadCount = MAX_THREADS();
    for (unsigned i = 0; i < innerThreadCount; i++)
    {
       controlThreads_.push_back(thread(innerthread));
diff --git a/cppForSwig/BlockDataManagerConfig.cpp b/cppForSwig/BlockDataManagerConfig.cpp
index fee75f71f..acfefc77a 100644
--- a/cppForSwig/BlockDataManagerConfig.cpp
+++ b/cppForSwig/BlockDataManagerConfig.cpp
@@ -20,6 +20,20 @@
 
 using namespace std;
 
+size_t MAX_THREADS()
+{
+   size_t cpu_threads = std::thread::hardware_concurrency();
+
+   if (!cpu_threads)
+      return 1;
+   // there are only 126 LMDB locks by default
+   // FIXME: need to increase number of LMDB locks
+   else if (cpu_threads > 126)
+      return 126;
+
+   return cpu_threads;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 //
 // NodeStatusStruct
diff --git a/cppForSwig/BlockDataManagerConfig.h b/cppForSwig/BlockDataManagerConfig.h
index ca064aef5..29b92dd9f 100644
--- a/cppForSwig/BlockDataManagerConfig.h
+++ b/cppForSwig/BlockDataManagerConfig.h
@@ -28,6 +28,8 @@
 #define DEFAULT_ZCTHREAD_COUNT 100
 #define WEBSOCKET_PORT 7681
 
+size_t MAX_THREADS();
+
 class BitcoinP2P;
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -66,7 +68,7 @@ struct BlockDataManagerConfig
    bool customBtcPort_ = false;
 
    unsigned ramUsage_ = 4;
-   unsigned threadCount_ = std::thread::hardware_concurrency();
+   unsigned threadCount_ = MAX_THREADS();
    unsigned zcThreadCount_ = DEFAULT_ZCTHREAD_COUNT;
 
    std::exception_ptr exceptionPtr_ = nullptr;
diff --git a/cppForSwig/Server.cpp b/cppForSwig/Server.cpp
index 85cb52045..0947eeedd 100644
--- a/cppForSwig/Server.cpp
+++ b/cppForSwig/Server.cpp
@@ -234,7 +234,7 @@ void WebSocketServer::start(BlockDataManagerThread* bdmT,
       instance->clientInterruptThread();
    };
 
-   unsigned parserThreads = thread::hardware_concurrency() / 4;
+   unsigned parserThreads = MAX_THREADS() / 4;
    if (parserThreads == 0)
       parserThreads = 1;
    for (unsigned i = 0; i < parserThreads; i++)
@@ -1038,4 +1038,4 @@ void ClientConnection::processAEADHandshake(BinaryData msg)
 void ClientConnection::closeConnection()
 {
    run_->store(-1, memory_order_relaxed);
-}
\ No newline at end of file
+}
diff --git a/cppForSwig/ZeroConf.cpp b/cppForSwig/ZeroConf.cpp
index 21251af03..4bee65c91 100644
--- a/cppForSwig/ZeroConf.cpp
+++ b/cppForSwig/ZeroConf.cpp
@@ -290,7 +290,7 @@ void ZeroConfContainer::preprocessZcMap(
    };
 
    vector<thread> parserThreads;
-   for (unsigned i = 1; i < thread::hardware_concurrency(); i++)
+   for (unsigned i = 1; i < MAX_THREADS(); i++)
       parserThreads.push_back(thread(parserLdb));
    parserLdb();
 
@@ -2111,4 +2111,4 @@ bool ZcUpdateBatch::hasData() const
       return true;
    
    return false;
-}
\ No newline at end of file
+}