Better signals interface

This avoids some CPP and accidentally using Unix stuff in client code.

src/libutil/unix/monitor-fd.hh

@@ -50,7 +50,7 @@ public:
                 */
                 if (count == 0) continue;
                 if (fds[0].revents & POLLHUP) {
-                    triggerInterrupt();
+                    unix::triggerInterrupt();
                     break;
                 }
                 /* This will only happen on macOS. We sleep a bit to

src/libutil/unix/signals-impl.hh

@@ -1,5 +1,14 @@
 #pragma once
-///@file
+/**
+ * @file
+ *
+ * Implementation of some inline definitions for Unix signals, and also
+ * some extra Unix-only interfaces.
+ *
+ * (The only reason everything about signals isn't Unix-only is some
+ * no-op definitions are provided on Windows to avoid excess CPP in
+ * downstream code.)
+ */
 
 #include "types.hh"
 #include "error.hh"
@@ -24,22 +33,20 @@ namespace nix {
 
 /* User interruption. */
 
+namespace unix {
+
 extern std::atomic<bool> _isInterrupted;
 
 extern thread_local std::function<bool()> interruptCheck;
 
-void setInterruptThrown();
-
 void _interrupted();
 
-void inline checkInterrupt()
-{
-    if (_isInterrupted || (interruptCheck && interruptCheck()))
-        _interrupted();
-}
-
-MakeError(Interrupted, BaseError);
-
+/**
+ * Sets the signal mask. Like saveSignalMask() but for a signal set that doesn't
+ * necessarily match the current thread's mask.
+ * See saveSignalMask() to set the saved mask to the current mask.
+ */
+void setChildSignalMask(sigset_t *sigs);
 
 /**
  * Start a thread that handles various signals. Also block those signals
@@ -63,27 +70,27 @@ void saveSignalMask();
  */
 void restoreSignals();
 
-/**
- * Sets the signal mask. Like saveSignalMask() but for a signal set that doesn't
- * necessarily match the current thread's mask.
- * See saveSignalMask() to set the saved mask to the current mask.
- */
-void setChildSignalMask(sigset_t *sigs);
-
-struct InterruptCallback
-{
-    virtual ~InterruptCallback() { };
-};
-
-/**
- * Register a function that gets called on SIGINT (in a non-signal
- * context).
- */
-std::unique_ptr<InterruptCallback> createInterruptCallback(
-    std::function<void()> callback);
-
 void triggerInterrupt();
 
+}
+
+static inline void setInterrupted(bool isInterrupted)
+{
+    unix::_isInterrupted = isInterrupted;
+}
+
+static inline bool getInterrupted()
+{
+    return unix::_isInterrupted;
+}
+
+void inline checkInterrupt()
+{
+    using namespace unix;
+    if (_isInterrupted || (interruptCheck && interruptCheck()))
+        _interrupted();
+}
+
 /**
  * A RAII class that causes the current thread to receive SIGUSR1 when
  * the signal handler thread receives SIGINT. That is, this allows

src/libutil/unix/signals.cc

@@ -8,17 +8,22 @@
 
 namespace nix {
 
-std::atomic<bool> _isInterrupted = false;
+using namespace unix;
 
+std::atomic<bool> unix::_isInterrupted = false;
+
+namespace unix {
 static thread_local bool interruptThrown = false;
-thread_local std::function<bool()> interruptCheck;
+}
+
+thread_local std::function<bool()> unix::interruptCheck;
 
 void setInterruptThrown()
 {
-    interruptThrown = true;
+    unix::interruptThrown = true;
 }
 
-void _interrupted()
+void unix::_interrupted()
 {
     /* Block user interrupts while an exception is being handled.
        Throwing an exception while another exception is being handled
@@ -65,7 +70,7 @@ static void signalHandlerThread(sigset_t set)
     }
 }
 
-void triggerInterrupt()
+void unix::triggerInterrupt()
 {
     _isInterrupted = true;
 
@@ -96,7 +101,7 @@ void triggerInterrupt()
 static sigset_t savedSignalMask;
 static bool savedSignalMaskIsSet = false;
 
-void setChildSignalMask(sigset_t * sigs)
+void unix::setChildSignalMask(sigset_t * sigs)
 {
     assert(sigs); // C style function, but think of sigs as a reference
 
@@ -115,14 +120,14 @@ void setChildSignalMask(sigset_t * sigs)
     savedSignalMaskIsSet = true;
 }
 
-void saveSignalMask() {
+void unix::saveSignalMask() {
     if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask))
         throw SysError("querying signal mask");
 
     savedSignalMaskIsSet = true;
 }
 
-void startSignalHandlerThread()
+void unix::startSignalHandlerThread()
 {
     updateWindowSize();
 
@@ -141,7 +146,7 @@ void startSignalHandlerThread()
     std::thread(signalHandlerThread, set).detach();
 }
 
-void restoreSignals()
+void unix::restoreSignals()
 {
     // If startSignalHandlerThread wasn't called, that means we're not running
     // in a proper libmain process, but a process that presumably manages its