bitcoin-core
diff --git a/‎doc/developer-notes.md
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diff --git a/‎src/Makefile.am
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diff --git a/‎src/Makefile.qt.include
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diff --git a/‎src/Makefile.qttest.include
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diff --git a/‎src/interface/README.md
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diff --git a/‎src/interface/handler.cpp
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diff --git a/‎src/interface/handler.h
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@@ -625,6 +625,19 @@ GUI
     should not interact with the user. That's where View classes come in. The converse also
     holds: try to not directly access core data structures from Views.
 
+- Avoid adding slow or blocking code in the GUI thread. In particular do not
+  add new `interface::Node` and `interface::Wallet` method calls, even if they
+  may be fast now, in case they are changed to lock or communicate across
+  processes in the future.
+
+  Prefer to offload work from the GUI thread to worker threads (see
+  `RPCExecutor` in console code as an example) or take other steps (see
+  https://doc.qt.io/archives/qq/qq27-responsive-guis.html) to keep the GUI
+  responsive.
+
+  - *Rationale*: Blocking the GUI thread can increase latency, and lead to
+    hangs and deadlocks.
+
 Subtrees
 ----------
 
 
@@ -7,6 +7,7 @@ DIST_SUBDIRS = secp256k1 univalue
 AM_LDFLAGS = $(PTHREAD_CFLAGS) $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS) $(GPROF_LDFLAGS) $(SANITIZER_LDFLAGS)
 AM_CXXFLAGS = $(HARDENED_CXXFLAGS) $(ERROR_CXXFLAGS) $(GPROF_CXXFLAGS) $(SANITIZER_CXXFLAGS)
 AM_CPPFLAGS = $(HARDENED_CPPFLAGS)
+AM_LIBTOOLFLAGS = --preserve-dup-deps
 EXTRA_LIBRARIES =
 
 if EMBEDDED_UNIVALUE
@@ -104,6 +105,9 @@ BITCOIN_CORE_H = \
   httpserver.h \
   indirectmap.h \
   init.h \
+  interface/handler.h \
+  interface/node.h \
+  interface/wallet.h \
   key.h \
   key_io.h \
   keystore.h \
@@ -245,6 +249,7 @@ endif
 libbitcoin_wallet_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_wallet_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_wallet_a_SOURCES = \
+  interface/wallet.cpp \
   wallet/crypter.cpp \
   wallet/db.cpp \
   wallet/feebumper.cpp \
@@ -357,6 +362,8 @@ libbitcoin_util_a_SOURCES = \
   compat/glibcxx_sanity.cpp \
   compat/strnlen.cpp \
   fs.cpp \
+  interface/handler.cpp \
+  interface/node.cpp \
   random.cpp \
   rpc/protocol.cpp \
   rpc/util.cpp \
 
@@ -402,7 +402,7 @@ if TARGET_WINDOWS
 endif
 qt_bitcoin_qt_LDADD = qt/libbitcoinqt.a $(LIBBITCOIN_SERVER)
 if ENABLE_WALLET
-qt_bitcoin_qt_LDADD += $(LIBBITCOIN_WALLET)
+qt_bitcoin_qt_LDADD += $(LIBBITCOIN_UTIL) $(LIBBITCOIN_WALLET)
 endif
 if ENABLE_ZMQ
 qt_bitcoin_qt_LDADD += $(LIBBITCOIN_ZMQ) $(ZMQ_LIBS)
@@ -411,7 +411,7 @@ qt_bitcoin_qt_LDADD += $(LIBBITCOIN_CLI) $(LIBBITCOIN_COMMON) $(LIBBITCOIN_UTIL)
   $(BOOST_LIBS) $(QT_LIBS) $(QT_DBUS_LIBS) $(QR_LIBS) $(PROTOBUF_LIBS) $(BDB_LIBS) $(SSL_LIBS) $(CRYPTO_LIBS) $(MINIUPNPC_LIBS) $(LIBSECP256K1) \
   $(EVENT_PTHREADS_LIBS) $(EVENT_LIBS)
 qt_bitcoin_qt_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(QT_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
-qt_bitcoin_qt_LIBTOOLFLAGS = --tag CXX
+qt_bitcoin_qt_LIBTOOLFLAGS = $(AM_LIBTOOLFLAGS) --tag CXX
 
 #locale/foo.ts -> locale/foo.qm
 QT_QM=$(QT_TS:.ts=.qm)
 
@@ -52,7 +52,7 @@ nodist_qt_test_test_bitcoin_qt_SOURCES = $(TEST_QT_MOC_CPP)
 
 qt_test_test_bitcoin_qt_LDADD = $(LIBBITCOINQT) $(LIBBITCOIN_SERVER)
 if ENABLE_WALLET
-qt_test_test_bitcoin_qt_LDADD += $(LIBBITCOIN_WALLET)
+qt_test_test_bitcoin_qt_LDADD += $(LIBBITCOIN_UTIL) $(LIBBITCOIN_WALLET)
 endif
 if ENABLE_ZMQ
 qt_test_test_bitcoin_qt_LDADD += $(LIBBITCOIN_ZMQ) $(ZMQ_LIBS)
 
@@ -0,0 +1,17 @@
+# Internal c++ interfaces
+
+The following interfaces are defined here:
+
+* [`Chain`](chain.h) — used by wallet to access blockchain and mempool state. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
+
+* [`Chain::Client`](chain.h) — used by node to start & stop `Chain` clients. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
+
+* [`Node`](node.h) — used by GUI to start & stop bitcoin node. Added in [#10244](https://github.com/bitcoin/bitcoin/pull/10244).
+
+* [`Wallet`](wallet.h) — used by GUI to access wallets. Added in [#10244](https://github.com/bitcoin/bitcoin/pull/10244).
+
+* [`Handler`](handler.h) — returned by `handleEvent` methods on interfaces above and used to manage lifetimes of event handlers.
+
+* [`Init`](init.h) — used by multiprocess code to access interfaces above on startup. Added in [#10102](https://github.com/bitcoin/bitcoin/pull/10102).
+
+The interfaces above define boundaries between major components of bitcoin code (node, wallet, and gui), making it possible for them to run in different processes, and be tested, developed, and understood independently. These interfaces are not currently designed to be stable or to be used externally.
@@ -0,0 +1,33 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interface/handler.h>
+
+#include <util.h>
+
+#include <boost/signals2/connection.hpp>
+#include <memory>
+#include <utility>
+
+namespace interface {
+namespace {
+
+class HandlerImpl : public Handler
+{
+public:
+    HandlerImpl(boost::signals2::connection connection) : m_connection(std::move(connection)) {}
+
+    void disconnect() override { m_connection.disconnect(); }
+
+    boost::signals2::scoped_connection m_connection;
+};
+
+} // namespace
+
+std::unique_ptr<Handler> MakeHandler(boost::signals2::connection connection)
+{
+    return MakeUnique<HandlerImpl>(std::move(connection));
+}
+
+} // namespace interface
@@ -0,0 +1,35 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_INTERFACE_HANDLER_H
+#define BITCOIN_INTERFACE_HANDLER_H
+
+#include <memory>
+
+namespace boost {
+namespace signals2 {
+class connection;
+} // namespace signals2
+} // namespace boost
+
+namespace interface {
+
+//! Generic interface for managing an event handler or callback function
+//! registered with another interface. Has a single disconnect method to cancel
+//! the registration and prevent any future notifications.
+class Handler
+{
+public:
+    virtual ~Handler() {}
+
+    //! Disconnect the handler.
+    virtual void disconnect() = 0;
+};
+
+//! Return handler wrapping a boost signal connection.
+std::unique_ptr<Handler> MakeHandler(boost::signals2::connection connection);
+
+} // namespace interface
+
+#endif // BITCOIN_INTERFACE_HANDLER_H