Resolve #13: Fix simulated network propagation

The simulated network was recursively calling push_block when
propagating blocks, which caused a lock timeout. Fix this issue by not
pushing a new block to the database that created it.

Also, replace the currently_propagating_block flag with boost's slot
blocker.

libraries/chain/database.cpp

@@ -128,11 +128,6 @@ std::vector<block_id_type> database::get_block_ids_on_fork(block_id_type head_of
  */
 bool database::push_block(const signed_block& new_block, uint32_t skip)
 { try {
-   /// TODO: the simulated network code will cause push_block to be called
-   /// recursively which in turn will cause the write lock to hang
-   if( new_block.block_num() == head_block_num() && new_block.id() == head_block_id() ) 
-      return false;
-
    return with_skip_flags( skip, [&](){ 
       return without_pending_transactions( [&]() {
          return with_write_lock( [&]() { 

tests/common/database_fixture.cpp

@@ -23,6 +23,7 @@
  */
 #include <boost/test/unit_test.hpp>
 #include <boost/program_options.hpp>
+#include <boost/signals2/shared_connection_block.hpp>
 
 #include <eos/chain/account_object.hpp>
 #include <eos/chain/producer_object.hpp>
@@ -151,9 +152,8 @@ void testing_network::connect_database(testing_database& new_database) {
    }
 
    // The new database is now in sync with any old ones; go ahead and connect the propagation signal.
-   databases[&new_database] = new_database.applied_block.connect([this](const signed_block& block) {
-      if (!currently_propagating_block)
-         propagate_block(block);
+   databases[&new_database] = new_database.applied_block.connect([this, &new_database](const signed_block& block) {
+      propagate_block(block, new_database);
    });
 }
 
@@ -165,11 +165,12 @@ void testing_network::disconnect_all() {
    databases.clear();
 }
 
-void testing_network::propagate_block(const signed_block& block) {
-   currently_propagating_block = true;
-   for (const auto& pair : databases)
+void testing_network::propagate_block(const signed_block& block, const testing_database& skip_db) {
+   for (const auto& pair : databases) {
+      if (pair.first == &skip_db) continue;
+      boost::signals2::shared_connection_block blocker(pair.second);
       pair.first->push_block(block);
-   currently_propagating_block = false;
+   }
 }
 
 } } // eos::chain

tests/common/database_fixture.hpp

@@ -240,11 +240,10 @@ class testing_network {
     * @brief Send a block to all databases in this network
     * @param block The block to send
     */
-   void propagate_block(const signed_block& block);
+   void propagate_block(const signed_block& block, const testing_database& skip_db);
 
 protected:
    std::map<testing_database*, fc::scoped_connection> databases;
-   bool currently_propagating_block = false;
 };
 
 /// Some helpful macros to reduce boilerplate when making a testing_network and connecting some testing_databases @{