Comment by pjmlp
1 day ago
Because that OS best practices is to use threads.
Traditionally Windows applications that create processes all the time come from UNIX heritage.
Contrary to UNIX, Windows NT was designed with threads first mentality, from the get go.
While on UNIX they were added after fact, and to this day there are gotchas mixing posix threads with signals, fork and exec.
A more accurate way to describe this is that Windows' (NT onward) core execution context model is a bunch of threads that by default share memory, whereas Unixen have a core task context model of a bunch of threads that by default do not share memory.
Both systems are implemented using threads as the execution context, but in Unix, the history means that that you fork+exec most of the time, resulting in a two tasks that do not share memory any more. By contrast, on Windows (NT onward) the common case when creating a new execution context is to create a thread that shares memory with others in its process.
Both systems allow the easy use of the other's core abstraction. On Unix, you can either code like its 1986 and use fork without exec, or use clone(3) or any of its higher level abstractions like pthreads.
You're right that POSIX semantics get tangled when using threads.
That's actually less accurate, not more. It's a post-hoc revision that conflates Unix with Linux.
The Unix model was invented over a decade before the idea of multithreading percolated into mainstream operating systems at all.
The reason that Windows NT started as it did, was that OS/2 had come out in 1987, with kernel threads, and the idea of multithreading had taken root. SunOS 5 gained threading, too.
Windows NT applications development began with threading available as a mechanism from the start, and with a lot of people in the IBM/Microsoft world already knowing about its use in applications development from OS/2.
Whereas with the Unices it came in more gradually, as the applications had often already been designed. The whole libthread versus libpthread thing made things interesting on SunOS for a few years, too. As did the first attempt (LinuxThreads) at providing threads on Linux.
PaulDavisThe1st is saying that the Unix pattern of forking a process (and not calling exec) was an early form of multi-threading (or multi-processing), but unlike threads in NT and later pthreads, they didn't share memory and communication between them required some form of IPC.
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Well, Windows before NT isn't the same design as Windows 16 bit, it only shares the name for all practical purposes, and has more influence from OS/2 than Windows 16 bit.
Which is why I took the effort to explicitly refer to Windows NT on my comment, already expecting some traditional answers from UNIX folks.
Also due to historical reasons POSIX threads are the outcome of every UNIX going their own way implementing threads, finally coming to an agreement years later, with all the plus and minus of relying in POSIX for portable code.
whereas Unixen have a core task context model of a bunch of threads that by default do not share memory.
How are those not simply child processes? I don't understand your use of the word 'threads' here.
Does the Unix world not distinguish between threads and processes? In Win32, threads exist within processes, and you can create new threads or child processes.
They are child processes.
Second answer: Linux doesn't differentiate between threads and processes. It has a "thread group ID" that serves a small number of purposes, and the rest of the difference is just whether the threads happen to share the same address space.
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Actually on Windows a process is a thread with additional information.
The unit of execution is the thread.
On the UNIX world it depends on which UNIX you are talking about.
Linux has a similar model to Windows NT nowadays, hence clone() as key primitive.
Other UNIXes have different approaches.
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POSIX threads having problems with signals is, imho, mostly the problem with signals in general. They are pretty poorly designed: https://lwn.net/Articles/414618/
The problem is that threads are not fault boundaries but processes are. So they're not interchangeable when you care about resilience and misbehaving code.
True, but on Windows the approach is then to use COM servers, which have a faster IPC model, and can even serve multiple clients, depending on how the appartement space is configured.
"Faster IPC model" than what? Faster than writing to and reading from a pipe? Faster than POSIX shared memory?
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If you want the isolation features of a separate process, you can’t substitute it with a single multithreaded COM server process.
.NET tried this with app domains, which are now deprecated.
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the only difference between a thread and a process on linux is how many structures they share. the function is identical.
Agreed, however not all UNIXes are like Linux.
Windows was designed with threads-first mentality because on pre-386 machines you don't have viable process memory protection, so your tasks share memory by necessity. This is not a great argument.
Windows NT was never designed with pre-386 machines in mind. That was the territory of the old DOS+Windows. Windows NT from the get-go was for machines with page-based virtual memory.
* https://computernewb.com/~lily/files/Documents/NTDesignWorkb...
WinNT 3.5 was a solid offering.
This is not true. NT never had fork, was always based on the assumption of an MMU and Dave Cutler was a well known fork hater in the 80s long before this paper came out and made it cool to be so. By the time Windows 95 was out, the baseline was 386 with an MMU. CreateThread was initially designed for NT in 1993 though (which didn’t support pre-386 CPUs).
As mentioned elsewhere on this page, Windows NT had fork from the start. Vide NtCreateProcess and what happens if an image file is not explicitly supplied.
* https://computernewb.com/~lily/files/Documents/NTDesignWorkb...
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NT performed unnatural acts to implement fork semantics for the POSIX subsystem.
NT was designed to be platform-agnostic, and its original target was the DEC Alpha. Its process model owes nothing to pre-386 CPUs. The WinAPI CreateProcess function is a layer atop NtCreateProcess, so that is where the pre-386 heritage lives. But even the WinAPI process model changed significantly with 32-bit Windows.
No.
https://en.wikipedia.org/wiki/Windows_NT#Development
Windows NT was developed on various different CPUs before the Alpha was a thing. When it was released in 1993, it was released for three CPUs: IA-32, MIPS, and Alpha.
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Windows NT!
Misread on purpose to make a point?