कोई अजीब-क्रमांकित विंडोज प्रक्रिया आईडी क्यों नहीं हैं?

2024 लेखक: Geoffrey Carr | [email protected]. अंतिम बार संशोधित: 2023-12-17 11:00

यदि आप विंडोज के साथ झुकाव करना पसंद करते हैं और सीखते समय सीखते हैं, तो आपने देखा होगा कि विंडोज़ प्रक्रिया और थ्रेड आईडी भी संख्याबद्ध हैं और चार के गुणक हैं। ऐसा क्यों है? आज के सुपर यूज़र क्यू एंड ए पोस्ट में एक जिज्ञासु पाठक के सवालों के जवाब हैं।

आज का प्रश्न और उत्तर सत्र हमारे पास सुपरयूसर की सौजन्य है - स्टैक एक्सचेंज का एक उपविभाग, क्यू एंड ए वेब साइट्स का एक समुदाय संचालित समूह।

प्रश्न

सुपर यूज़र रीडर पीटर हैन्डॉर्फ़ जानना चाहता है कि क्यों कोई अजीब संख्या वाली विंडोज प्रक्रिया आईडी नहीं है:


There are many ways to look at the process IDs in Windows. Using PowerShell:



I get this result:




As you can see, all the process IDs are even-numbered, not only that, they are all multiples of four. You can look as hard as you want and you will never find an odd-numbered process ID, at least not on any version that is Windows NT-based. What is the reason for this?

कोई अजीब संख्या वाली विंडोज प्रक्रिया आईडी क्यों नहीं हैं?

उत्तर

SuperUser योगदानकर्ता डेविडपोस्टिल का जवाब हमारे लिए है:


Why are there no odd-numbered Windows process IDs?
The same code that allocates kernel handles is also used to allocate process and thread IDs. Since kernel handles are a multiple of four, so are process and thread IDs.
Why are process and thread IDs multiples of four?
On Windows NT-based operating systems, process and thread IDs always happen to be a multiple of four. Is this just a coincidence?
Yes, it is just a coincidence, and you should not rely on it since it is not part of the programming contract. For example, Windows 95 process and thread IDs were not always multiples of four. By comparison, the reason that kernel handles are always a multiple of four is part of the specification and will be guaranteed for the foreseeable future.
Process and thread IDs are multiples of four as a side-effect of code reuse. The same code that allocates kernel handles is also used to allocate process and thread IDs. Since kernel handles are multiples of four, so are process and thread IDs. This is an implementation detail, so do not write code that relies on it. I am just telling you to satisfy your curiosity.
Source: Why are process and thread IDs multiples of four?
Why are kernel handles always a multiple of four?
Something that is not very well known is that the bottom two bits of kernel handles are always zero; in other words, their numeric value is always a multiple of four. Note that this applies only to kernel handles; it does not apply to pseudo-handles or to any other type of handle (USER handles, GDI handles, multimedia handles, etc.). Kernel handles are things you can pass to the CloseHandle function.



That at least the bottom bit of kernel handles are always zero is implied by the GetQueuedCompletionStatus function, which indicates that you can set the bottom bit of the event handle to suppress completion port notification. In order for this to work, the bottom bit must normally be zero.

This information is not useful for most application writers, which should continue to treat handles as opaque values. The people who would be interested in tag bits are those who are implementing low-level class libraries or are wrapping kernel objects inside a larger framework.
Source: Why are kernel handles always a multiple of four?
Further Reading
The Old New Thing: Practical Development Throughout the Evolution of Windows by Raymond Chen (Principal Software Design Engineer at Microsoft)

स्पष्टीकरण में जोड़ने के लिए कुछ है? टिप्पणियों में विचार व्यक्त करो। अन्य तकनीक-समझदार स्टैक एक्सचेंज उपयोगकर्ताओं से अधिक उत्तरों पढ़ना चाहते हैं? यहां पूर्ण चर्चा धागा देखें।