PCLSRing - Revision history

Larsbrinkhoff: Early PCLSRing code from ITS 1.0!

2023-11-23T06:50:05Z

Early PCLSRing code from ITS 1.0!

Jnc: /* External links */ This except is shorter

2023-07-29T02:28:28Z

‎External links: This except is shorter

Jnc: /* External links */ give actual doc with PCLSRing discussion

2023-07-28T21:03:19Z

‎External links: give actual doc with PCLSRing discussion

Larsbrinkhoff: Link to RPG's Worse Is Better.

2023-07-28T15:00:13Z

Link to RPG's Worse Is Better.

Larsbrinkhoff: /* External links */ The PCLOSER Problem, by Ron Lebel.

2022-04-20T10:59:58Z

‎External links: The PCLOSER Problem, by Ron Lebel.

Jnc: rm dup link

2021-08-19T15:14:29Z

rm dup link

Jnc: +links, Ext links, cat

2021-08-19T14:23:57Z

+links, Ext links, cat

Larsbrinkhoff: Create stub.

2021-08-19T07:24:02Z

Create stub.

New page

'''PCLSRing''' means PC-lusering, from [[program counter]] and [[luser]], the [[ITS]] jargon for [[user]].

It's the process of ensuring that the PC of a [[process]] is in user space. This makes it easier for one process to observe and reason about another process, because the observed process does not exhibit any state hidden in kernel space.

PCLSRing is mostly associated with the [[ITS]] operating system. In some form it can also be found in the [[Berkeley Timesharing System]] and [[SITS]].

If a process is executing in kernel space and needs to be PCLSRed, typical strategies are:

* Update the user space state and return immediately. This can only be done in special cases when the user state can express the intermediate state of a kernel operation. An example is an I/O read/write operation where user space state includes the I/O length and target address.
* Back out the side effects of a kernel operation and return to a user space point before the operation was started.

A strategy not considered proper PCLSRing is to cancel the kernel operation and return an error to user space. This was the topic of the essay known as "Worse Is Better".

{{stub}}

← Older revision		Revision as of 06:50, 23 November 2023
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	'''PCLSRing''' means PC-lusering (from [[Program Counter]] and [[luser]], the [[Incompatible Timesharing System\|ITS]] jargon for [[user]]).		'''PCLSRing''' means PC-lusering (from [[Program Counter]] and [[luser]], the [[Incompatible Timesharing System\|ITS]] jargon for [[user]]).
		+
		+	[[Image:PCLSR.png\|thumb\|right\|400px\|Early PCLSRing code from ITS 1.0.]]

	It's the procedure of ensuring that the PC of a [[process]] is in user space. This makes it easier for one process to observe and reason about another process, because the observed process does not exhibit any state hidden in [[kernel]] space.		It's the procedure of ensuring that the PC of a [[process]] is in user space. This makes it easier for one process to observe and reason about another process, because the observed process does not exhibit any state hidden in [[kernel]] space.

@@ Line 18: / Line 18: @@
 * [http://fare.tunes.org/tmp/emergent/pclsr.htm PCLSRing: Keeping Process State Modular] - Alan Bawden's detailed memo on PCLSRing
 * [https://github.com/larsbrinkhoff/mit-logo-and-sits-raw-files/blob/master/files/19741205_2of3_AI_KA_Arch_1113-1116_1117p/rjl/ch3.2 The PCLOSER Problem] - Ron Lebel's writeup for SITS.
-* [https://www.dreamsongs.com/Files/LispGoodNewsBadNews.pdf Lisp: Good News, Bad News, How to Win Big] - PCLSRing is discussed in Section 2.1, "The Rise of Worse is Better"
+* [https://www.dreamsongs.com/RiseOfWorseIsBetter.html The Rise of Worse is Better] - the philosophy of PCLSRing is discussed in this except of "Lisp: Good News, Bad News, How to Win Big"
 ** [https://www.dreamsongs.com/WorseIsBetter.html Worse Is Better] - background
 [[Category: OS Basics]]

@@ Line 11: / Line 11: @@
 A strategy not considered proper PCLSRing is to cancel the kernel operation and return an error to user space.  This was the topic of the essay known as "Worse Is Better".
 ==External links==
@@ Line 16: / Line 18: @@
 * [http://fare.tunes.org/tmp/emergent/pclsr.htm PCLSRing: Keeping Process State Modular] - Alan Bawden's detailed memo on PCLSRing
 * [https://github.com/larsbrinkhoff/mit-logo-and-sits-raw-files/blob/master/files/19741205_2of3_AI_KA_Arch_1113-1116_1117p/rjl/ch3.2 The PCLOSER Problem] - Ron Lebel's writeup for SITS.
-* [https://www.dreamsongs.com/WorseIsBetter.html Worse Is Better] by Richard P. Gabriel.
+* [https://www.dreamsongs.com/Files/LispGoodNewsBadNews.pdf Lisp: Good News, Bad News, How to Win Big] - PCLSRing is discussed in Section 2.1, "The Rise of Worse is Better"
+** [https://www.dreamsongs.com/WorseIsBetter.html Worse Is Better] - background
 [[Category: OS Basics]]

@@ Line 16: / Line 16: @@
 * [http://fare.tunes.org/tmp/emergent/pclsr.htm PCLSRing: Keeping Process State Modular] - Alan Bawden's detailed memo on PCLSRing
 * [https://github.com/larsbrinkhoff/mit-logo-and-sits-raw-files/blob/master/files/19741205_2of3_AI_KA_Arch_1113-1116_1117p/rjl/ch3.2 The PCLOSER Problem] - Ron Lebel's writeup for SITS.
 {{semi-stub}}
 [[Category: OS Basics]]

@@ Line 15: / Line 15: @@
 * [http://fare.tunes.org/tmp/emergent/pclsr.htm PCLSRing: Keeping Process State Modular] - Alan Bawden's detailed memo on PCLSRing
 {{semi-stub}}
 [[Category: OS Basics]]

@@ Line 1: / Line 1: @@
-'''PCLSRing''' means PC-lusering (from [[Program Counter]] and [[luser]], the [[ITS]] jargon for [[user]]).
+'''PCLSRing''' means PC-lusering (from [[Program Counter]] and [[luser]], the [[Incompatible Timesharing System|ITS]] jargon for [[user]]).
 It's the procedure of ensuring that the PC of a [[process]] is in user space.  This makes it easier for one process to observe and reason about another process, because the observed process does not exhibit any state hidden in [[kernel]] space.
-PCLSRing is mostly associated with the [[ITS]] [[operating system]].  In some form it can also be found in the [[Berkeley Timesharing System]] and [[SITS]].
+PCLSRing is mostly associated with the ITS [[operating system]].  In some form it can also be found in the [[Berkeley Timesharing System]] and [[SITS]].
 If a process is executing in kernel space and needs to be PCLSRed, typical strategies are: