Page 355 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes
Figure 12.2: The Relationship Between Jobs, Processes and Threads. Several Fibers
can also be Multiplexed on One Thread (not shown)

Although we will not discuss it in much detail, Windows 2000 is capable of running on
a symmetric multiprocessor system. This requirement means that the operating system
code must be fully reentrant, that is, every procedure must be written in such a way that
two or more CPUs may be changing its variables at once, without causing problems. In
many cases, this means that code sections have to be protected by spin locks or mutexes
to keep additional CPUs at bay until the first one is done (i.e., serialize access to critical
regions). The number of CPUs the system can handle is governed by the licensing
restrictions. There is no technical reason why Windows Professional cannot run on a
32-node multiprocessor, it is the same binary as Datacenter Server, after all.

The upper limit of 32 CPUs is a hard limit because word-length bitmaps are used to keep track
of CPU usage in various ways. For example, one word-length bitmap keeps track of which of the
(up to) 32 CPUs are currently idle, and another bitmap is used per process to list the CPUs this
process is permitted to run on. The 64-bit version of Windows 2000 should be able to effortlessly
support up to 64 CPUs; beyond that requires actually changing the code substantially (to use
multiple words for the bitmaps).
12.1.2 Job, Process, Thread and Fiber Management API Calls

New processes are created using the Win32 API function CreateProcess. This function has
10 parameters, each of which has many options. This design is clearly much more complicated
than the UNIX scheme, in which fork has no parameters, and exec has just three: pointers to the
name of the file to execute: the (parsed) command line parameter array, and the environment
strings. Roughly speaking, the 10 parameters to CreateProcess are as follows:
1. A pointer to the name of the executable file.
2. The command line itself (unparsed).

3. A pointer to a security descriptor for the process.
4. A pointer to a security descriptor for the initial thread.
5. A bit telling whether the new process inherits the creator’s handles.

6. Miscellaneous flags (e.g., error mode, priority, debugging, consoles).

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