Add File > Fetch > Cancel Fetch menu item.

4 files changed, 98 insertions, 70 deletions

diff --git a/c/data.cpp b/c/data.cpp
index da5df7a..d9401c9 100644
--- a/c/data.cpp
+++ b/c/data.cpp
@@ -5,15 +5,11 @@
 #include <libxml/HTMLtree.h>
 #include <libxml/xpath.h>
 
+#include "resource.h"
 #include "data.h"
 #include "episodelistview.h"
 #include "win.h"
 
-/* Signals for thread communication. */
-constexpr unsigned char SIG_READY = 1<<0;
-constexpr unsigned char SIG_DONE = 1<<1;
-constexpr unsigned char SIG_ABORT = 1<<2;
-
 struct XmlError : public std::exception
 {
 	const char* msg;
@@ -93,6 +89,80 @@ bool WcharsFromXmlchars(wchar_t (&dst)[N], XmlCharPtr utf8) noexcept
 	return MultiByteToWideChar(CP_UTF8, 0, src, cchNarrow, dst, cchWide);
 }
 
+/* The Fetch* functions are run in a separate thread via WaitFor. The
+ * main thread and the fetch thread communicate by setting flags on a
+ * shared byte. At any given time, only a single fetch thread may be
+ * performing work. */
+
+enum Signal
+{
+	READY = 1<<0,	/* Main -> fetch: start working! */
+	DONE = 1<<1,	/* Fetch -> main: work is done. */
+	ABORT = 1<<2	/* Main -> fetch: exit prematurely! */
+};
+
+void WaitFor(void (*f)(unsigned char*))
+{
+	extern HWND g_hWnd;
+	static unsigned char sig = READY;
+	static UINT_PTR iTimer = 0;
+
+	static auto procTimer = [](HWND, UINT, UINT_PTR, DWORD) -> void
+	{
+		static int i = 0;
+
+		if (sig & DONE) {
+			extern EpisodeListView* const g_elv;
+			KillTimer(nullptr, iTimer);
+			i = 0;
+			sig = READY; /* Reset signals. */
+			g_elv->Update(); /* Reset status bar. */
+			EnableMenuItem(GetMenu(g_hWnd), IDM_FILE_FETCH_CANCEL, MF_GRAYED);
+		} else {
+			/* Animate ellipsis in status bar. */
+			static const wchar_t* text[] = {L".", L"..", L"...", L""};
+			i = (i+1)%(sizeof(text)/sizeof(*text));
+			Status(text[i], 1);
+		}
+	};
+
+	static auto procThread = [](void (*f)(unsigned char*)) noexcept -> void
+	{
+		while (!(sig & READY))
+			Sleep(100);
+		sig = 0;
+		EnableMenuItem(GetMenu(g_hWnd), IDM_FILE_FETCH_CANCEL, MF_ENABLED);
+		try {
+			f(&sig);
+			sig |= DONE;
+		} catch (...) {
+			sig |= DONE;
+			ShowException(L"Remote data could not be fetched due to an error: %s",
+			    L"Error", MB_ICONWARNING);
+		}
+	};
+
+	/* Null indicates that any active task should be cancelled. */
+	if (!f) {
+		sig |= ABORT;
+		return;
+	}
+
+	/* Ensure that only a single thread is waited on. */
+	if (!(sig & READY)) {
+		if (EBMessageBox(L"Another task is active. "
+		    L"Do you want to cancel the existing task and start a new one?",
+		    L"Error", MB_YESNO|MB_ICONWARNING) == IDYES)
+			sig |= ABORT;
+		else
+			return;
+	}
+
+	std::thread(procThread, f).detach();
+	Status(L".", 1);
+	Prefer(iTimer = SetTimer(nullptr, iTimer, 500, procTimer));
+}
+
 void FetchData(unsigned char* sig)
 {
 	/* The remote data is retrieved using WinINet from the
@@ -118,7 +188,7 @@ void FetchData(unsigned char* sig)
 		extern FileView<ElvDataA> g_fvElv;
 		extern FileView<DlvDataA> g_fvDlv;
 
-		if (*sig & SIG_ABORT)
+		if (*sig & ABORT)
 			return;
 
 		const xmlNodePtr node = nodes->nodeTab[i];
@@ -160,10 +230,16 @@ void FetchScreenwriters(unsigned char* sig)
 	extern FileView<DlvDataA> g_fvDlv;
 	extern CfgA& g_cfg;
 
+	/* Screenwriters are expensive to fetch, so we try to avoid
+	 * fetching screenwriters for episodes that already have a
+	 * screenwriter. Additionally, in the same session, we don't
+	 * try to fetch screenwriters for episodes for which we have
+	 * already tried to fetch screenwriters. We keep track of
+	 * these states using the iLast variable. */
 	static int iLast = -1;
 	int iMax = g_cfg.cEp-1;
 
-	/* Find the last fetched screenwriter. */
+	/* Find the last episode that has a screenwriter. */
 	if (iLast == -1)
 		for (size_t i = 0; i < g_fvDlv.c; i++)
 			if (const DlvDataA& d = g_fvDlv[i]; !d.date[0]) {
@@ -179,7 +255,7 @@ void FetchScreenwriters(unsigned char* sig)
 	wchar_t url[256];
 	Wcscpy(url, prefix);
 	for (iLast++; iLast < iMax; iLast++) {
-		if (*sig & SIG_ABORT)
+		if (*sig & ABORT)
 			return;
 
 		wchar_t msg[48];
@@ -197,64 +273,9 @@ void FetchScreenwriters(unsigned char* sig)
 		    "//th[contains(text(), 'Screenplay:')]/following-sibling::td"),
 		    xpathCtx);
 		xmlNodeSetPtr nodes = xpathObj->nodesetval;
-		if (!nodes || !nodes->nodeNr)
-			continue;
-		xmlChar* s = xmlNodeGetContent(nodes->nodeTab[0]);
-		WcharsFromXmlchars(d.screenwriter, s);
-	}
-}
-
-void WaitFor(void (*f)(unsigned char*))
-{
-	static unsigned char sig = SIG_READY;
-	static UINT_PTR iTimer = 0;
-
-	/* The timer procedure animates an ellipsis in the status bar
-	 * while the thread is running. */
-	static auto procTimer = [](HWND, UINT, UINT_PTR, DWORD) -> void
-	{
-		static int i = 0;
-		static const wchar_t* text[] = {L".", L"..", L"...", L""};
-
-		if (sig & SIG_DONE) {
-			extern EpisodeListView* const g_elv;
-			KillTimer(nullptr, iTimer);
-			i = 0;
-			sig &= ~SIG_DONE;
-			sig |= SIG_READY;
-			g_elv->Update(); /* Reset status bar. */
-		} else {
-			i = (i+1)%(sizeof(text)/sizeof(*text));
-			Status(text[i], 1);
+		if (nodes && nodes->nodeNr) {
+			xmlChar* s = xmlNodeGetContent(nodes->nodeTab[0]);
+			WcharsFromXmlchars(d.screenwriter, s);
 		}
-	};
-
-	static auto procThread = [](void (*f)(unsigned char*)) noexcept -> void
-	{
-		while (!(sig & SIG_READY))
-			Sleep(100);
-		sig &= ~SIG_READY;
-		try {
-			f(&sig);
-			sig |= SIG_DONE;
-		} catch (...) {
-			sig |= SIG_DONE;
-			ShowException(L"Remote data could not be fetched due to an error: %s",
-			    L"Error", MB_ICONWARNING);
-		}
-	};
-
-	/* Ensure that only a single thread is waited on. */
-	if (!(sig & SIG_READY)) {
-		if (EBMessageBox(L"Another task is active. "
-		    L"Do you want to cancel the existing task and start a new one?",
-		    L"Error", MB_YESNO|MB_ICONWARNING) == IDYES)
-			sig |= SIG_ABORT;
-		else
-			return;
 	}
-
-	std::thread(procThread, f).detach();
-	Status(L".", 1);
-	Prefer(iTimer = SetTimer(nullptr, iTimer, 500, procTimer));
 }
diff --git a/c/main.cpp b/c/main.cpp
index 5935ee1..244d1fe 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -312,6 +312,7 @@ LRESULT CALLBACK HandleMsg(const HWND hWnd, const UINT uMsg, const WPARAM wParam
 			/*IDM_FILE_REFRESH*/L"Quickly refresh episode list.",
 			/*IDM_FILE_FETCH_DATA*/L"Fetch episode data from the web (may take a few seconds).",
 			/*IDM_FILE_FETCH_SCREENWRITERS*/L"Fetch screenwriters from the web (may take a minute).",
+			/*IDM_FILE_FETCH_CANCEL*/L"Stop fetching data from the web.",
 			/*IDM_FILE_ABOUT*/L"Show information about Episode Browser.",
 			/*IDM_VIEW_WATCHED*/(g_cfg.bViewWatched?
 			    L"Click to hide watched episodes.":
@@ -395,6 +396,10 @@ void HandleMainMenu(const HWND hWnd, const WORD command)
 		WaitFor(FetchScreenwriters);
 		break;
 
+	case IDM_FILE_FETCH_CANCEL:
+		WaitFor(nullptr);
+		break;
+
 	case IDM_FILE_ABOUT:
 		DialogBox(
 		    GetModuleHandle(nullptr),
diff --git a/c/resource.h b/c/resource.h
index 3bf23b0..50490bc 100644
--- a/c/resource.h
+++ b/c/resource.h
@@ -31,10 +31,11 @@
 #define IDM_FILE_REFRESH       		0x0301
 #define IDM_FILE_FETCH_DATA		0x0302
 #define IDM_FILE_FETCH_SCREENWRITERS	0x0303
-#define IDM_FILE_ABOUT			0x0304
-#define IDM_VIEW_WATCHED       		0x0305
-#define IDM_VIEW_TV_ORIGINAL		0x0306
-#define IDM_VIEW_OTHERS			0x0307
+#define IDM_FILE_FETCH_CANCEL		0x0304
+#define IDM_FILE_ABOUT			0x0305
+#define IDM_VIEW_WATCHED       		0x0306
+#define IDM_VIEW_TV_ORIGINAL		0x0307
+#define IDM_VIEW_OTHERS			0x0308
 
 /* Context menu items. */
 #define IDM_WATCH_LOCALLY		0x0400
diff --git a/c/resource.rc b/c/resource.rc
index 2b7a9a7..acecce4 100644
--- a/c/resource.rc
+++ b/c/resource.rc
@@ -11,6 +11,7 @@ BEGIN
 		BEGIN
 			MENUITEM "&General Data", IDM_FILE_FETCH_DATA
 			MENUITEM "&Screenwriters", IDM_FILE_FETCH_SCREENWRITERS
+			MENUITEM "&Cancel Fetch", IDM_FILE_FETCH_CANCEL, GRAYED
 		END
 		MENUITEM "&Refresh", IDM_FILE_REFRESH
 		MENUITEM "E&xit", IDM_FILE_EXIT