\n\nThe \nWhy do you need to clean up one-shot timers?\n<\/P>\n \nTo answer this, I would like to introduce you to one of my\nfavorite rhetorical questions when trying to puzzle out\nAPI design:\n“What would the world be like if this were true?”\n<\/P>\n \nImagine what the world would be like if you didn’t need to\nclean up one-shot timers.\n<\/P>\n \nWell, for one thing, it means that the behavior of the\nfunction would be confusing. The caller of the\nthe \nBut far, far worse is that if one-shot timers were self-deleting,\nit would be impossible to use them correctly.\n<\/P>\n \nSuppose you have an object that creates a one-shot timer,\nand you want to clean it up in your destructor if it hasn’t fired yet.\nIf one-shot timers were self-deleting,\nthen it would be impossible to write this object.\n<\/P>\n \nYou might say, “Well, I’ll have my callback null out the\n \nExcept that’s a race condition.\n<\/P>\n \nIf the callback is pre-empted during the race window\nand the object is destructed,\nand one-shot timers were self-deleting,\nthen the object would attempt to use an invalid handle.\n<\/P>\n \nThis race window is uncloseable\nsince the race happens even before\nyou get a chance to execute a single line of code.\n<\/P>\n \nSo be glad that you have to delete handles to one-shot timers.\n<\/P><\/p>\n","protected":false},"excerpt":{"rendered":" The CreateTimerQueueTimer function allows you to create one-shot timers by passing the WT_EXECUTEONLYONCE flag. The documentation says that you need to call the DeleteTimerQueueTimer function when you no longer need the timer. Why do you need to clean up one-shot timers? To answer this, I would like to introduce you to one of my favorite […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-36913","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":" The CreateTimerQueueTimer function allows you to create one-shot timers by passing the WT_EXECUTEONLYONCE flag. The documentation says that you need to call the DeleteTimerQueueTimer function when you no longer need the timer. Why do you need to clean up one-shot timers? To answer this, I would like to introduce you to one of my favorite […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/36913","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=36913"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/36913\/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=36913"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=36913"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=36913"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}CreateTimerQueueTimer<\/CODE> function<\/A> allows you to create\none-shot timers by passing\nthe WT_EXECUTEONLYONCE<\/CODE> flag.\nThe documentation says that\nyou need to call\n\nthe DeleteTimerQueueTimer<\/CODE> function<\/A>\nwhen you no longer need the timer.\n<\/P>\nCreateTimerQueueTimer<\/CODE> function would have\nto keep track of whether the timer was one-shot or not,\nto know whether or not the handle needed to be deleted.\n<\/P>\n\nclass Sample {\n HANDLE m_hTimer;\n Sample() : m_hTimer(NULL) { CreateTimerQueueTimer(&m_hTimer, …); }\n ~Sample() { … what to write here? … }\n};\n<\/PRE>\n m_hTimer<\/CODE> variable. That way, the destructor\nwill know that the timer has fired.”\n<\/P>\n\nSample::Callback(void *context)\n{\n \/\/\/ RACE WINDOW HERE\n ((Sample*)context)->m_hTimer = NULL;\n …\n}\n<\/PRE>\n