Better signals interface

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

src/libcmd/repl.cc

@@ -357,7 +357,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
     if (line.empty())
         return ProcessLineResult::PromptAgain;
 
-    _isInterrupted = false;
+    setInterrupted(false);
 
     std::string command, arg;
 

src/libfetchers/git-utils.cc

@@ -348,7 +348,7 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
     {
         auto act = (Activity *) payload;
         act->result(resFetchStatus, trim(std::string_view(str, len)));
-        return _isInterrupted ? -1 : 0;
+        return getInterrupted() ? -1 : 0;
     }
 
     static int transferProgressCallback(const git_indexer_progress * stats, void * payload)
@@ -361,7 +361,7 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
                 stats->indexed_deltas,
                 stats->total_deltas,
                 stats->received_bytes / (1024.0 * 1024.0)));
-        return _isInterrupted ? -1 : 0;
+        return getInterrupted() ? -1 : 0;
     }
 
     void fetch(

src/libmain/shared.cc

@@ -121,7 +121,7 @@ void initNix()
 
     initLibStore();
 
-    startSignalHandlerThread();
+    unix::startSignalHandlerThread();
 
     /* Reset SIGCHLD to its default. */
     struct sigaction act;

src/libstore/daemon.cc

@@ -1,5 +1,6 @@
 #include "daemon.hh"
 #include "monitor-fd.hh"
+#include "signals.hh"
 #include "worker-protocol.hh"
 #include "worker-protocol-impl.hh"
 #include "build-result.hh"
@@ -1038,7 +1039,7 @@ void processConnection(
     unsigned int opCount = 0;
 
     Finally finally([&]() {
-        _isInterrupted = false;
+        setInterrupted(false);
         printMsgUsing(prevLogger, lvlDebug, "%d operations", opCount);
     });
 

src/libstore/filetransfer.cc

@@ -258,11 +258,11 @@ struct curlFileTransfer : public FileTransfer
         int progressCallback(double dltotal, double dlnow)
         {
             try {
-              act.progress(dlnow, dltotal);
+                act.progress(dlnow, dltotal);
             } catch (nix::Interrupted &) {
-              assert(_isInterrupted);
+                assert(getInterrupted());
             }
-            return _isInterrupted;
+            return getInterrupted();
         }
 
         static int progressCallbackWrapper(void * userp, double dltotal, double dlnow, double ultotal, double ulnow)
@@ -466,7 +466,7 @@ struct curlFileTransfer : public FileTransfer
                 if (errorSink)
                     response = std::move(errorSink->s);
                 auto exc =
-                    code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
+                    code == CURLE_ABORTED_BY_CALLBACK && getInterrupted()
                     ? FileTransferError(Interrupted, std::move(response), "%s of '%s' was interrupted", request.verb(), request.uri)
                     : httpStatus != 0
                     ? FileTransferError(err,

src/libutil/current-process.cc

@@ -82,7 +82,7 @@ void setStackSize(rlim_t stackSize)
 
 void restoreProcessContext(bool restoreMounts)
 {
-    restoreSignals();
+    unix::restoreSignals();
     if (restoreMounts) {
         #if __linux__
         restoreMountNamespace();

src/libutil/signals.hh

@@ -0,0 +1,70 @@
+#pragma once
+///@file
+
+#include "types.hh"
+#include "error.hh"
+#include "logging.hh"
+
+#include <functional>
+
+namespace nix {
+
+/* User interruption. */
+
+/**
+ * @note Does nothing on Windows
+ */
+static inline void setInterrupted(bool isInterrupted);
+
+/**
+ * @note Does nothing on Windows
+ */
+static inline bool getInterrupted();
+
+/**
+ * @note Does nothing on Windows
+ */
+static inline void setInterruptCheck(std::function<bool()> interruptCheck);
+
+/**
+ * @note Does nothing on Windows
+ */
+void setInterruptThrown();
+
+/**
+ * @note Does nothing on Windows
+ */
+inline void checkInterrupt();
+
+/**
+ * @note Never will happen on Windows
+ */
+MakeError(Interrupted, BaseError);
+
+
+struct InterruptCallback
+{
+    virtual ~InterruptCallback() { };
+};
+
+/**
+ * Register a function that gets called on SIGINT (in a non-signal
+ * context).
+ *
+ * @note Does nothing on Windows
+ */
+std::unique_ptr<InterruptCallback> createInterruptCallback(
+    std::function<void()> callback);
+
+/**
+ * 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.
+ *
+ * @note Does nothing on Windows
+ */
+struct ReceiveInterrupts;
+
+}
+
+#include "signals-impl.hh"

src/libutil/thread-pool.cc

@@ -82,7 +82,7 @@ void ThreadPool::doWork(bool mainThread)
     ReceiveInterrupts receiveInterrupts;
 
     if (!mainThread)
-        interruptCheck = [&]() { return (bool) quit; };
+        unix::interruptCheck = [&]() { return (bool) quit; };
 
     bool didWork = false;
     std::exception_ptr exc;

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.hh → 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
@@ -63,26 +70,26 @@ 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);
+void triggerInterrupt();
 
-struct InterruptCallback
+}
+
+static inline void setInterrupted(bool isInterrupted)
 {
-    virtual ~InterruptCallback() { };
-};
+    unix::_isInterrupted = isInterrupted;
+}
 
-/**
- * Register a function that gets called on SIGINT (in a non-signal
- * context).
- */
-std::unique_ptr<InterruptCallback> createInterruptCallback(
-    std::function<void()> callback);
+static inline bool getInterrupted()
+{
+    return unix::_isInterrupted;
+}
 
-void triggerInterrupt();
+void inline checkInterrupt()
+{
+    using namespace unix;
+    if (_isInterrupted || (interruptCheck && interruptCheck()))
+        _interrupted();
+}
 
 /**
  * A RAII class that causes the current thread to receive SIGUSR1 when

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