The implementation of critical sections in Windows has changed over the years, but it has always been a combination of user-mode and kernel calls.<\/p>\n
The CRITICAL_SECTION is a structure that contains a user-mode updated values, a handle to a kernel-mode object – EVENT or something like that, and debug information.<\/p>\n
EnterCriticalSection uses an interlocked test-and-set operation to acquire the lock. If successful, this is all that is required (almost, it also updates the owner thread). If the set-and-set operation fails to aquire, a longer path is used which usually requires waiting on a kernel object with Below is a diassembly of the “fast” \/ uncontended path of So the bottom line is that if the thread does not need to block it will not use a system call, just an interlocked test-and-set operation. If blocking is required, there will be a system call. The release path also uses an interlocked test-and-set and may require a system call if other threads are blocked.<\/p>\n Compare this to Mutex which always requires a system call The implementation of critical sections in Windows has changed over the years, but it has always been a combination of user-mode and kernel calls. The CRITICAL_SECTION is a structure that contains a user-mode updated values, a handle to a kernel-mode object – EVENT or something like that, and debug information. EnterCriticalSection uses an interlocked test-and-set […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4993","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4993","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=4993"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4993\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=4993"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=4993"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=4993"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}WaitForSignleObject<\/code>. If you initialized with InitializeCriticalSectionAndSpinCount<\/code> then EnterCriticalSection<\/code> may spin an retry to acquire using interlocked operation in user-mode.<\/p>\nEnterCriticialSection<\/code> in Windows 7 (64-bit) with some comments inline<\/p>\n0:000> u rtlentercriticalsection rtlentercriticalsection+35\nntdll!RtlEnterCriticalSection:\n00000000`77ae2fc0 fff3 push rbx\n00000000`77ae2fc2 4883ec20 sub rsp,20h\n; RCX points to the critical section rcx+8 is the LockCount\n00000000`77ae2fc6 f00fba710800 lock btr dword ptr [rcx+8],0\n00000000`77ae2fcc 488bd9 mov rbx,rcx\n00000000`77ae2fcf 0f83e9b1ffff jae ntdll!RtlEnterCriticalSection+0x31 (00000000`77ade1be)\n; got the critical section - update the owner thread and recursion count\n00000000`77ae2fd5 65488b042530000000 mov rax,qword ptr gs:[30h]\n00000000`77ae2fde 488b4848 mov rcx,qword ptr [rax+48h]\n00000000`77ae2fe2 c7430c01000000 mov dword ptr [rbx+0Ch],1\n00000000`77ae2fe9 33c0 xor eax,eax\n00000000`77ae2feb 48894b10 mov qword ptr [rbx+10h],rcx\n00000000`77ae2fef 4883c420 add rsp,20h\n00000000`77ae2ff3 5b pop rbx\n00000000`77ae2ff4 c3 ret\n<\/code><\/pre>\nNtWaitForSingleObject<\/code> and NtReleaseMutant<\/code><\/p>\n","protected":false},"excerpt":{"rendered":"