From 83ae6503e87c7f5237fb0f1602793c126436495a Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 25 Jan 2017 13:37:02 +0100
Subject: [PATCH] Fix interrupt handling

---
 src/libmain/shared.cc     |  9 +++++++++
 src/libutil/monitor-fd.hh |  3 +--
 src/libutil/util.cc       | 26 +++++++++++++++-----------
 src/libutil/util.hh       | 16 ++++++++++++++++
 4 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 12f083c7f..d564e0385 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -97,6 +97,9 @@ static void opensslLockCallback(int mode, int type, const char * file, int line)
 }
 
 
+static void sigHandler(int signo) { }
+
+
 void initNix()
 {
     /* Turn on buffering for cerr. */
@@ -130,6 +133,10 @@ void initNix()
     if (sigaction(SIGCHLD, &act, 0))
         throw SysError("resetting SIGCHLD");
 
+    /* Install a dummy SIGUSR1 handler for use with pthread_kill(). */
+    act.sa_handler = sigHandler;
+    if (sigaction(SIGUSR1, &act, 0)) throw SysError("handling SIGUSR1");
+
     /* Register a SIGSEGV handler to detect stack overflows. */
     detectStackOverflow();
 
@@ -253,6 +260,8 @@ void showManPage(const string & name)
 
 int handleExceptions(const string & programName, std::function<void()> fun)
 {
+    ReceiveInterrupts receiveInterrupts; // FIXME: need better place for this
+
     string error = ANSI_RED "error:" ANSI_NORMAL " ";
     try {
         try {
diff --git a/src/libutil/monitor-fd.hh b/src/libutil/monitor-fd.hh
index 6f01ccd91..e0ec66c01 100644
--- a/src/libutil/monitor-fd.hh
+++ b/src/libutil/monitor-fd.hh
@@ -27,8 +27,7 @@ public:
             fds[0].events = 0;
             if (poll(fds, 1, -1) == -1) abort(); // can't happen
             assert(fds[0].revents & POLLHUP);
-            /* We got POLLHUP, so send an INT signal to the main thread. */
-            kill(getpid(), SIGINT);
+            triggerInterrupt();
         });
     };
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 52608ac2a..ca4edc2cd 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1197,18 +1197,22 @@ static void signalHandlerThread(sigset_t set)
         int signal = 0;
         sigwait(&set, &signal);
 
-        if (signal == SIGINT || signal == SIGTERM || signal == SIGHUP) {
-            _isInterrupted = 1;
+        if (signal == SIGINT || signal == SIGTERM || signal == SIGHUP)
+            triggerInterrupt();
+    }
+}
 
-            {
-                auto interruptCallbacks(_interruptCallbacks.lock());
-                for (auto & callback : *interruptCallbacks) {
-                    try {
-                        callback();
-                    } catch (...) {
-                        ignoreException();
-                    }
-                }
+void triggerInterrupt()
+{
+    _isInterrupted = 1;
+
+    {
+        auto interruptCallbacks(_interruptCallbacks.lock());
+        for (auto & callback : *interruptCallbacks) {
+            try {
+                callback();
+            } catch (...) {
+                ignoreException();
             }
         }
     }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index b68d48582..07141ffed 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -433,5 +433,21 @@ struct InterruptCallback
 std::unique_ptr<InterruptCallback> createInterruptCallback(
     std::function<void()> callback);
 
+void triggerInterrupt();
+
+/* A RAII class that causes the current thread to receive SIGUSR1 when
+   the signal handler thread receives SIGINT. That is, this allows
+   SIGINT to be multiplexed to multiple threads. */
+struct ReceiveInterrupts
+{
+    pthread_t target;
+    std::unique_ptr<InterruptCallback> callback;
+
+    ReceiveInterrupts()
+        : target(pthread_self())
+        , callback(createInterruptCallback([&]() { pthread_kill(target, SIGUSR1); }))
+    { }
+};
+
 
 }