{"id":35963,"date":"2005-04-06T08:56:57","date_gmt":"2005-04-06T08:56:57","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2005\/04\/06\/the-dialog-manager-part-7-more-subtleties-in-message-loops\/"},"modified":"2005-04-06T08:56:57","modified_gmt":"2005-04-06T08:56:57","slug":"the-dialog-manager-part-7-more-subtleties-in-message-loops","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20050406-57\/?p=35963","title":{"rendered":"The dialog manager, part 7: More subtleties in message loops"},"content":{"rendered":"

\n\nLast time, we solved the problem with\nthe EndManualModalDialog<\/code> function\nby posting a harmless message<\/a>.\nToday, we’re going to solve the problem in an entirely\ndifferent way.\n<\/p>\n

\nThe idea here is to make sure the modal message loop\nregains control, even if all that happened were incoming\nsent messages, so that it can detect that the fEnded<\/code>\nflag is set and break out of the modal loop.\n<\/p>\n

\nInstead of changing\nthe EndManualModalDialog<\/code> function,\nwe will change the modal message loop.\n<\/p>\n

\nint DoModal(HWND hwnd)\n{\n DIALOGSTATE ds = { 0 };\n HWND hdlg = CreateDialogParam(g_hinst, MAKEINTRESOURCE(1),\n             hwnd, DlgProc, reinterpret_cast<LPARAM>(&ds));\n if (!hdlg) {\n  return -1;\n }\n EnableWindow(hwnd, FALSE);\n MSG msg;\n msg.message = WM_NULL; \/\/ anything that isn't WM_QUIT\n while (!ds.fEnded<\/font>) {\n  if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {\n   if (msg.message == WM_QUIT) { \/*  fixed 8am *\/\n    break;\n   } else<\/font> if (!IsDialogMessage(hdlg, &msg)) {\n    TranslateMessage(&msg);\n    DispatchMessage(&msg);\n   } \/* fixed 10am *\/\n  } else if (!ds.fEnded) {\n   WaitMessage();\n  }<\/font>\n }\n if (msg.message == WM_QUIT) {\n  PostQuitMessage((int)msg.wParam);\n }\n EnableWindow(hwnd, TRUE);\n DestroyWindow(hdlg);\n return ds.iResult;\n}\n<\/pre>\n
\nWe changed the call to GetMessage<\/code>\ninto a call to\n\nthe PeekMessage<\/code> function<\/a>,\nasking to remove the peeked message if any.\nLike GetMessage<\/code>,\nthis delivers any incoming sent messages,\nthen checks if there are any posted messages in the queue.\nThe difference is that whereas GetMessage<\/code>\nkeeps waiting if there are no posted message,\nPeekMessage<\/code> returns and tells you that there\nwere no posted messages.\n<\/p>\n
\nThat’s the control we want.\nIf PeekMessage<\/code> says that it couldn’t\nfind a posted message, we check our fEnded<\/code>\nflag once again, in case an incoming sent message\nset the fEnded<\/code> flag.\nIf not, then we call\n\nthe WaitMessage<\/code> function<\/a>\nto wait until there is something to do\n(either an incoming sent message or a posted message).\n<\/p>\n
\nExercise: If the whole point was to regain control\nafter sent messages are delivered, why isn’t there a test\nof the fEnded<\/code> flag immediately after\nDispatchMessage<\/code> returns?<\/p>\n","protected":false},"excerpt":{"rendered":"
Last time, we solved the problem with the EndManualModalDialog function by posting a harmless message. Today, we’re going to solve the problem in an entirely different way. The idea here is to make sure the modal message loop regains control, even if all that happened were incoming sent messages, so that it can detect that […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-35963","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Last time, we solved the problem with the EndManualModalDialog function by posting a harmless message. Today, we’re going to solve the problem in an entirely different way. The idea here is to make sure the modal message loop regains control, even if all that happened were incoming sent messages, so that it can detect that […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/35963","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=35963"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/35963\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=35963"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=35963"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=35963"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}