core_tests: reset thread pool between tests

Avoids a DB error (leading to an assert) where a thread uses
a read txn previously created with an environment that was
since closed and reopened. While this usually works since
BlockchainLMDB renews txns if it detects the environment has
changed, this will not work if objects end up being allocated
at the same address as the previous instance, leading to stale
data usage.

Thanks hyc for the LMDB debugging.

2 files changed, 27 insertions, 7 deletions

diff --git a/src/common/threadpool.cpp b/src/common/threadpool.cpp
index 2748c798c..6eb527cdc 100644
--- a/src/common/threadpool.cpp
+++ b/src/common/threadpool.cpp
@@ -37,16 +37,14 @@ static __thread bool is_leaf = false;
 namespace tools
 {
 threadpool::threadpool(unsigned int max_threads) : running(true), active(0) {
-  boost::thread::attributes attrs;
-  attrs.set_stack_size(THREAD_STACK_SIZE);
-  max = max_threads ? max_threads : tools::get_max_concurrency();
-  size_t i = max ? max - 1 : 0;
-  while(i--) {
-    threads.push_back(boost::thread(attrs, boost::bind(&threadpool::run, this, false)));
-  }
+  create(max_threads);
 }
 
 threadpool::~threadpool() {
+  destroy();
+}
+
+void threadpool::destroy() {
   try
   {
     const boost::unique_lock<boost::mutex> lock(mutex);
@@ -64,6 +62,23 @@ threadpool::~threadpool() {
     try { threads[i].join(); }
     catch (...) { /* ignore */ }
   }
+  threads.clear();
+}
+
+void threadpool::recycle() {
+  destroy();
+  create(max);
+}
+
+void threadpool::create(unsigned int max_threads) {
+  boost::thread::attributes attrs;
+  attrs.set_stack_size(THREAD_STACK_SIZE);
+  max = max_threads ? max_threads : tools::get_max_concurrency();
+  size_t i = max ? max - 1 : 0;
+  running = true;
+  while(i--) {
+    threads.push_back(boost::thread(attrs, boost::bind(&threadpool::run, this, false)));
+  }
 }
 
 void threadpool::submit(waiter *obj, std::function<void()> f, bool leaf) {
diff --git a/src/common/threadpool.h b/src/common/threadpool.h
index 5e490ee7d..a49d0e14f 100644
--- a/src/common/threadpool.h
+++ b/src/common/threadpool.h
@@ -69,12 +69,17 @@ public:
   // task to finish.
   void submit(waiter *waiter, std::function<void()> f, bool leaf = false);
 
+  // destroy and recreate threads
+  void recycle();
+
   unsigned int get_max_concurrency() const;
 
   ~threadpool();
 
   private:
     threadpool(unsigned int max_threads = 0);
+    void destroy();
+    void create(unsigned int max_threads);
     typedef struct entry {
       waiter *wo;
       std::function<void()> f;