Optionally disable pipeline halt on SIGINT (#154)

Optional argument `signal_halt` for the `G3Pipeline.Run()` method.  By default, this is set to True to enable current behavior, namely that a pipeline is halted (via the `halt_processing` flag) and terminates after the current frame reaches the end of the pipeline.  If False, this signal handling is disabled, and it is then up to the user to ensure that a running pipeline is properly halted on interrupt.

core/include/core/G3Pipeline.h

@@ -32,7 +32,7 @@ class G3Pipeline {
 
 	// Run the pipeline to completion. If profile is set to true, will print
 	// statistics for each module at completion.
-	void Run(bool profile = false, bool graph = false);
+	void Run(bool profile = false, bool graph = false, bool signal_halt = true);
 
 	// If there is stored graph information get it
 	std::string GetGraphInfo() const {

core/src/G3Pipeline.cxx

@@ -212,7 +212,7 @@ G3Pipeline::siginfo_catcher(int)
 #endif
 
 void
-G3Pipeline::Run(bool profile, bool graph)
+G3Pipeline::Run(bool profile, bool graph, bool signal_halt)
 {
 	struct rusage last_rusage;
 	std::vector<G3Pipeline_mod_data> mods;
@@ -239,12 +239,14 @@ G3Pipeline::Run(bool profile, bool graph)
 		getrusage(RUSAGE_THREAD, &last_rusage);
 #endif
 
-	// Catch SIGINT
-	sigint_catcher.sa_handler = &G3Pipeline::sigint_catcher;
-	sigint_catcher.sa_flags = SA_RESTART | SA_RESETHAND;
-	sigemptyset(&sigint_catcher.sa_mask);
-	sigaddset(&sigint_catcher.sa_mask, SIGINT);
-	sigaction(SIGINT, &sigint_catcher, &oldsigint);
+	if (signal_halt) {
+		// Catch SIGINT
+		sigint_catcher.sa_handler = &G3Pipeline::sigint_catcher;
+		sigint_catcher.sa_flags = SA_RESTART | SA_RESETHAND;
+		sigemptyset(&sigint_catcher.sa_mask);
+		sigaddset(&sigint_catcher.sa_mask, SIGINT);
+		sigaction(SIGINT, &sigint_catcher, &oldsigint);
+	}
 
 #ifdef SIGINFO
 	if (profile) {
@@ -288,7 +290,8 @@ G3Pipeline::Run(bool profile, bool graph)
 
 	// Restore old handler
 	G3Pipeline::halt_processing = false;
-	sigaction(SIGINT, &oldsigint, &sigint_catcher);
+	if (signal_halt)
+		sigaction(SIGINT, &oldsigint, &sigint_catcher);
 #ifdef SIGINFO
 	if (profile)
 		sigaction(SIGINFO, &oldsiginfo, &siginfo_catcher);

core/src/python.cxx

@@ -578,17 +578,20 @@ SPT3G_PYTHON_MODULE(core)
 	  "\t  processing if returned by first module. Equivalent to [].\n")
 	    .def("_Add_", &G3Pipeline::Add, bp::arg("name")="")
 	    .def("Run", &G3Pipeline::Run,
-	      (bp::arg("profile")=false, bp::arg("graph")=false), 
+	      (bp::arg("profile")=false, bp::arg("graph")=false,
+	       bp::arg("signal_halt")=true),
 	      "Run pipeline. If profile is True, print execution time "
 	      "statistics for each module when complete. If graph is True, "
 	      "stores control flow data that can be processed with GraphViz "
-	      "once retrieved using GetGraphInfo().")
+	      "once retrieved using GetGraphInfo().  If signal_halt is True "
+	      "(default), the pipeline will stop processing new frames when "
+	      "SIGINT is sent to this process.  Equivalent to what happens when "
+	      "halt_processing() is called.")
 	    .def("GetGraphInfo", &G3Pipeline::GetGraphInfo,
 	      "Get stored control flow information from Run(graph=True)")
 	    .def("halt_processing", &G3Pipeline_halt_processing,
 	      "Halts all running pipelines after they flush all currently "
-	      "in-flight frames. Equivalent to what happens when SIGINT is "
-	      "sent to this process. Once set, the first module will not be "
+	      "in-flight frames. Once set, the first module will not be "
 	      "called again.")
 	    .staticmethod("halt_processing")
 	    .def_readonly("last_frame",