Handle exceptions in fetching thread.

7 files changed, 63 insertions, 41 deletions

diff --git a/c/data.cpp b/c/data.cpp
index 4bded44..771e6fb 100644
--- a/c/data.cpp
+++ b/c/data.cpp
@@ -70,7 +70,7 @@ static inline void XmlFree(void* p) { xmlFree(p); }
 using XmlCharPtr = XmlPtr<XmlFree, xmlChar*>;
 
 template <size_t N>
-bool WcharsFromXmlchars(wchar_t (&dst)[N], XmlCharPtr utf8)
+bool WcharsFromXmlchars(wchar_t (&dst)[N], XmlCharPtr utf8) noexcept
 {
 	/* Truncate if source is larger than destination. */
 	int lenUtf8 = xmlStrlen(utf8);
@@ -94,7 +94,7 @@ bool WcharsFromXmlchars(wchar_t (&dst)[N], XmlCharPtr utf8)
 	return MultiByteToWideChar(CP_UTF8, 0, src, cchNarrow, dst, cchWide);
 }
 
-void FetchData(bool* bDone)
+void FetchData()
 {
 	LIBXML_TEST_VERSION;
 
@@ -123,7 +123,9 @@ void FetchData(bool* bDone)
 	xmlNodeSetPtr nodes = xpathObj->nodesetval;
 	int cNodes = nodes? nodes->nodeNr: 0;
 
-	printf("%d nodes\n", cNodes);
+	if (!cNodes)
+		throw std::runtime_error("could not find remote episode information");
+
 	for (int i = 0; i < cNodes; i++) {
 		extern FileView<ElvDataA> g_fvElv;
 		extern FileView<DlvDataA> g_fvDlv;
@@ -153,8 +155,18 @@ void FetchData(bool* bDone)
 		/* Get wiki URL. */
 		const xmlNodePtr nodeLink = xmlFirstElementChild(nodeTitle);
 		if (nodeLink)
-			WcharsFromXmlchars(d.wiki, xmlGetProp(nodeLink, (const xmlChar*)"href"));
+			WcharsFromXmlchars(d.wiki,
+			    xmlGetProp(nodeLink, reinterpret_cast<const xmlChar*>("href")));
 	}
+}
 
-	*bDone = true;
+void WaitFetchData(bool* bDone) noexcept
+{
+	try {
+		FetchData();
+		*bDone = true;
+	} catch (...) {
+		*bDone = true;
+		ShowException(L"Remote data could not be fetched due to %s: %s", L"Error", MB_ICONWARNING);
+	}
 }
diff --git a/c/data.h b/c/data.h
index 4e0d97a..23c9e5f 100644
--- a/c/data.h
+++ b/c/data.h
@@ -9,6 +9,10 @@
 #include "wcharptr.h"
 #include "win.h"
 
+/* Fetch data from the web. */
+void FetchData();
+void WaitFetchData(bool* bDone) noexcept;
+
 /* The structs ending with A are written as-is to disk. As such, they
  * should be regarded as immutable. If the format needs to be changed
  * in the future, then new structs ending with B should be added. */
@@ -162,9 +166,6 @@ struct FileView
 	size_t c;
 };
 
-/* Fetch data from the web. */
-void FetchData(bool* bDone);
-
 inline int FromWeb(const int iEp, ElvDataA& e, DlvDataA& d) noexcept
 {
 	WcharPtr title, wiki, date, source, hint;
diff --git a/c/main.cpp b/c/main.cpp
index d6e3027..73a89d4 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -24,7 +24,7 @@
 
 /* Exit gracefully on uncaught exception. */
 static void OnTerminate() noexcept;
-static auto unused = std::set_terminate(OnTerminate);
+static auto UNUSED = std::set_terminate(OnTerminate);
 
 /* main.cpp defines all global (non-template) variables used in the
  * program. `extern' is used to access them from other files, when
@@ -81,29 +81,7 @@ static void UpdateTheme();
 
 void OnTerminate() noexcept
 {
-	const wchar_t* what = L"an exception";
-	WcharPtr why;
-
-	try {
-		std::rethrow_exception(std::current_exception());
-        } catch (const term_t& t) {
-		what = L"a Prolog exception";
-		try { why = PlString(t); } catch (...) {}
-	} catch (const Win32Error& e) {
-		what = L"a Windows error";
-		try { why = WcharPtr::Copy(e.What()); } catch (...) {}
-	} catch (const std::exception& e) {
-		try { why = WcharPtr::FromNarrow(e.what()); } catch (...) {}
-	} catch (...) {}
-
-	wchar_t msg[256] = {0};
-	if (why)
-		Swprintf(msg, L"Episode Browser was terminated due to %s: %s",
-		    what, static_cast<wchar_t*>(why));
-	else
-		Swprintf(msg, L"Episode Browser was terminated due to %s.", what);
-
-	MessageBox(g_hWnd, msg, L"Fatal Error", MB_ICONERROR);
+	ShowException(L"Episode Browser was terminated due to %s: %s", L"Fatal Error", MB_ICONERROR);
 	_Exit(1);
 }
 
@@ -402,7 +380,7 @@ void HandleMainMenu(const HWND hWnd, const WORD command)
 
 	case IDM_FILE_FETCH_DATA:
 	    {
-		WaitFor(FetchData);
+		WaitFor(WaitFetchData);
 		break;
 	    }
 
@@ -456,13 +434,11 @@ void HandleMainMenu(const HWND hWnd, const WORD command)
 
 void WaitFor(void (*f)(bool*))
 {
-	/* WaitFor uses a thread on the Prolog side to execute a
-	 * predicate asynchronously. */
-
 	static bool bActive = false;
 	static bool bDone = false;
 	static UINT_PTR iTimer;
 
+	/* Ensure that only a single thread is waited on. */
 	if (bActive) {
 		if (EBMessageBox(L"Another task is active. "
 		    L"Do you want to cancel the existing task and start a new one?",
@@ -476,7 +452,6 @@ void WaitFor(void (*f)(bool*))
 
 	/* The timer procedure animates an ellipsis in the status bar
 	 * while the thread is running. */
-
 	static auto proc = [](HWND, UINT, UINT_PTR, DWORD) -> void
 	{
 		static int i = 0;
@@ -494,6 +469,8 @@ void WaitFor(void (*f)(bool*))
 		}
 	};
 
+	/* The waited-on function signals its completion by setting a
+	 * shared boolean value to true. */
 	bDone = false;
 	bActive = true;
 	std::thread{f, &bDone}.detach();
diff --git a/c/test.cpp b/c/test.cpp
index d784367..7d6b3ed 100644
--- a/c/test.cpp
+++ b/c/test.cpp
@@ -16,9 +16,7 @@ struct Test
 	Test(const char* name) : name(name) {}
 };
 
-#define CAT(a, b) a##b
-#define APPLY(a, ...) a(__VA_ARGS__)
-#define TESTS struct APPLY(CAT, tests_, __COUNTER__)
+#define TESTS struct UNUSED
 #define TEST(id) }; struct id : public Test { id() : Test(#id)
 #define FAIL(...) do { Sprintf(error, __VA_ARGS__); return; } while (0)
 
@@ -226,7 +224,7 @@ TESTS
 	TEST(Fetch)
 	{
 		bool bDone = false;
-		std::thread{FetchData, &bDone}.detach();
+		std::thread{WaitFetchData, &bDone}.detach();
 	}
 };
 
diff --git a/c/util.h b/c/util.h
index d233ce1..1d8d222 100644
--- a/c/util.h
+++ b/c/util.h
@@ -4,6 +4,12 @@
 #include <algorithm>
 #include <cstring>
 #include <memory>
+#include <SWI-Prolog.h>
+#include <windows.h>
+
+#define CAT(a, b) a##b
+#define APPLY(a, ...) a(__VA_ARGS__)
+#define UNUSED APPLY(CAT, unused_, __COUNTER__)
 
 /* Format static wide string. */
 template<size_t N, typename... T>
diff --git a/c/win.cpp b/c/win.cpp
index 28dba27..ea47fb0 100644
--- a/c/win.cpp
+++ b/c/win.cpp
@@ -1,7 +1,33 @@
 #include <utility>
+#include <SWI-Prolog.h>
 #include <windows.h>
 
+#include "pl.h"
+#include "util.h"
 #include "win.h"
+#include "wcharptr.h"
+
+void ShowException(const wchar_t* const fmt, const wchar_t* const title, const UINT uType) noexcept
+{
+	const wchar_t* what = L"an exception";
+	WcharPtr why;
+
+	try {
+		std::rethrow_exception(std::current_exception());
+        } catch (const term_t& t) {
+		what = L"a Prolog exception";
+		try { why = PlString(t); } catch (...) {}
+	} catch (const Win32Error& e) {
+		what = L"a Windows error";
+		try { why = WcharPtr::Copy(e.What()); } catch (...) {}
+	} catch (const std::exception& e) {
+		try { why = WcharPtr::FromNarrow(e.what()); } catch (...) {}
+	} catch (...) {}
+
+	wchar_t msg[512];
+	Swprintf(msg, fmt, what, static_cast<wchar_t*>(why));
+	EBMessageBox(msg, title, uType);
+}
 
 void WithNextWindow(void (*proc)(HWND))
 {
diff --git a/c/win.h b/c/win.h
index 93b1416..3bb0d6e 100644
--- a/c/win.h
+++ b/c/win.h
@@ -5,6 +5,8 @@
 #include <string_view>
 #include <windows.h>
 
+/* Show message box for current exception. */
+void ShowException(const wchar_t* fmt, const wchar_t* title, UINT uType = MB_ICONWARNING) noexcept;
 /* Run given procedure at creation of next window. */
 void WithNextWindow(void (*proc)(HWND));
 /* Display message box centered in main window. */