{"id":973,"date":"2014-05-16T07:00:00","date_gmt":"2014-05-16T07:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2014\/05\/16\/an-extensible-interlocked-arithmetic-function-via-lambdas\/"},"modified":"2014-05-16T07:00:00","modified_gmt":"2014-05-16T07:00:00","slug":"an-extensible-interlocked-arithmetic-function-via-lambdas","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20140516-00\/?p=973","title":{"rendered":"An extensible interlocked arithmetic function (via lambdas)"},"content":{"rendered":"

\nSome time ago, I noted that\n\nyou can build other interlocked operations out of\nInterlocked­Compare­Exchange<\/code><\/a>.\nHere’s an example:\n<\/p>\n

\nusing System.Threading;\npublic static int InterlockedMax(ref int location, int value)\n{\n    int initialValue, newValue;\n    do\n    {\n        initialValue = location;\n        newValue = Math.Max(initialValue, value);\n    }\n    while (Interlocked.CompareExchange(ref location, newValue,\n                                       initialValue) != initialValue);\n    return initialValue;\n}\n<\/pre>\n
\n(There’s a corresponding C++ version, which I leave as an exercise.)\n<\/p>\n
\nThis function atomically updates a “highest value seen so far” variable.\nIt follows the usual pattern:\n<\/p>\n
    \n
  • Capture the starting value.\n
  • Do a computation based on that value.\n
  • Compare-exchange the new value in.\n
  • If the compare-exchange failed, then start over.\n<\/ul>\n
    \n(For bonus points, add an\nearly-out if the operation should be abandoned.)\n<\/p>\n
    \nYou can make this function extensible by use of lambdas,\nso that you can update the old value with any computation you like.\n<\/p>\n
    \nusing System;\nusing System.Threading;\npublic static int InterlockedCombine(ref int location,\n                                     Func<int, int> update)\n{\n    int initialValue, newValue;\n    do\n    {\n        initialValue = location;\n        newValue = update(initialValue);\n    }\n    while (Interlocked.CompareExchange(ref location, newValue,\n                                       initialValue) != initialValue);\n    return initialValue;\n}\npublic static int InterlockedMax(ref int location, int value)\n{\n    return InterlockedCombine(ref location,\n                              v => Math.Max(v, value));\n}\npublic static int InterlockedMultiply(ref int location, int value)\n{\n    return InterlockedCombine(ref location,\n                              v => v * value);\n}\npublic static int InterlockedIncrementWithSaturation(\n    ref int location, int maximum)\n{\n    return InterlockedCombine(ref location,\n                              v => v < maximum ? v + 1 : maximum);\n}\npublic static int InterlockedCompareExchangeIfNotEqual(\n    ref int location, int newValue, int avoidValue)\n{\n    return InterlockedCombine(ref location,\n                              v => v != avoidValue ? newValue : avoidValue);\n}\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
    Some time ago, I noted that you can build other interlocked operations out of Interlocked­Compare­Exchange. Here’s an example: using System.Threading; public static int InterlockedMax(ref int location, int value) { int initialValue, newValue; do { initialValue = location; newValue = Math.Max(initialValue, value); } while (Interlocked.CompareExchange(ref location, newValue, initialValue) != initialValue); return initialValue; } (There’s a corresponding […]<\/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-973","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
    Some time ago, I noted that you can build other interlocked operations out of Interlocked­Compare­Exchange. Here’s an example: using System.Threading; public static int InterlockedMax(ref int location, int value) { int initialValue, newValue; do { initialValue = location; newValue = Math.Max(initialValue, value); } while (Interlocked.CompareExchange(ref location, newValue, initialValue) != initialValue); return initialValue; } (There’s a corresponding […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/973","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=973"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/973\/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=973"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=973"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=973"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}