The most important technical material to teach in an OSS course is how to read.
Most comp sci students have much too little exposure to real, large-scale software systems. This kind of a class is a perfect opportunity to expose them to large software. Even better, as an assignment they could read enough code to be able to make a change that doesn't break existing functionality, and hopefully adds more. It's a much harder process than most CS grads understand to change software withouth pissing off users.
But that's precisely the reason you musn't use locals: they are not preserved. The switch in the "thread" setup sets up a new scope in which you might declare locals, but that scope need not be entered cleanly, leading to (in the case of your example) an uninitialized local variable.
In your second example, the compiler *cannot* remove the sub-expression because the case statement that gets you there crosses a basic block boundary; the return statement from the blocking code, and the jump in through the switch are caught as valid C constructs that prevent the common sub-expression optimization.
The macros as given give you a semblance of variable continuity and scoping, but the compiler, after the macro substitutions, just sees a return on the end of the blocking section, and a switch into the code following, something like:
char YourFunc(char foo) { switch (foo) { case 'A':/*your blocking code*/ return 'B'; case 'B':/* the stuff after your blocking code */ break; } }
The ugliness in the macros is about letting other control constructs live around your switch in, but still generates legit code, but, for example, you can't use a local varible as an index to your for loop. Yuck.
The absence of local variables is because the stack is not preserved between invocations, and multiple invocations give the appearance of scheduled threads. There is nothing here that the compiler can break with its optimizer, unless it is breaking valid C code: the control flow expressed using the macros is completely legit C control flow. It's worth running the examples through just the C pre-processor in order to understand what gets built.
It's ugly as sin, but your compiler had better get it right, or else it's not a C compiler.
The challenge is making the design maintainable. There isn't a program that can't be written as a state machine; but most programs expressed this way are difficult to understand and maintain.
The argument that Rob Pike makes in A Concurrent Window System and with Luca Cardelli in Squeak: a Language for Communicating with Mice is that many of the event systems and associated state machines that we write can be much simplified by treating input multiplexing, and thus coroutine-like structures, as language primitives.
This work follows directly from Hoare's Communicating Sequential Processes - a good summary can be found here. Working with CSP only a little has convinced me of how much easier so many systems tasks are in this framework than in the world of the massive state-system/event loop world.
The macros compile out; you get a switch on a piece of state. Do yourself a favour, compile one of the examples and read the code generated. It's screaming efficient compared to a thread context switch.
I'd say the opposite; I use dashboard and spotlight *much* more than I expected. I have piles of documentation for a system I have to code that comes in ~100 PDFs that are non-printable. Spotlight finds my API and user guide sections for whatever I'm doing near-instantly. I use it to search in my code; I use it to find all the crap that I thought it couldn't index so well.
And dashboard! I get my stock prices at my fingertips - I'm a chronic reloader, and this is too easy. I keep clocks around for all the people I have to collaborate who are in different time zones. I keep the current weather at both ends of my commute visible (sometimes the distant weather has an effect on when I start my commute - it's right there to see in a hurry).
I recently ripped my 500 or so CDs. Took about 2 weeks of flipping disks when I walked by. No big deal.
The space savings is huge though: the amp is hidden in a closet, and iTunes runs on an Airport Express. All other components are gone. I don't need to even have shelving for the CDs. Net savings is a wall-slot for a new book case.
*ALL* console architectures require that the developer is quite aware of the architecture. If you're not, your competition will eat your shorts.
Heck, PC games require the developer to be very aware of the architecture; that's how they tune for performance; consoles just tend not to look quite like a PC, and thinking of them as PCs is just asking to produce (technically) poor games.
Frankly, I'd be extatic if more PC programmers paid attention to the changes in architecture that have been happenning in the last few years: memory bandwidth is now king, much more so than processor speed. But few optimize their code for the bus...
But no, you haven't violated the DMCA - you would need to distribute the crack. As I understand it, DMCA challenges that did not include actual copyright enfringement have failed.
You should probably purchase a second copy of the packaged goods to install on the second machine though:-)
Um, Try Oberon, or even Smalltalk in any decent implementation.
Object-oriented interactive shells are pretty common, and pretty much all of them provide interfaces the the system.
Hell, some of them even support pointy-clicky stuff.
I'm wondering if these changes to the future are limited to your observer's point of view. The future may well change, but only in ways that will not be observable to said observer. Then truth goes and gets even more relative.
It's the same question as asking if Schroedinger's cat notices if it is alive or dead. I assume it does, but that doesn't affect the outside observer.
Please explain how presenting ID does anything at all to increase passenger safety.
I was at a tallships festival where people were required to present ID before being allowed on board. Volunteers looked at the ID, nodded, and let you on. WTF?
ID does not certify someone not to be a whacked out nut job.
I got burned in the stock crash a few years ago; for reasons that aren't entirely rational I seem to trust real estate better than some other investments. And on top of, my local market has interesting constraints leading to a 10 year up-and-up...
I believe in living my life to open up options, not shut them down. The argument that city property drops in value doesn't hold: low-end city property might drop, but middle to high rarely does on the time scale we work in. Those parts of cities have died that way were industrial worker neighbourhoods destroyed by the advent of the automobile and passing of manufacturing jobs.
So again, tell me why you think high-value enforced savings plans in one's youth are wrong?
This idea that rural sourcing is good for employees is a fallacy.
An anectode: a friend of mine was offered two faculty positions, one in a rural setting and one in a large city. The salary was a little higher in the large city. When the rural school argued "but homes here cost only $100k, but they cost $300k in the city" my friend answered: "then it's clear, I must accept the position in the city". "But why?" "Because in 20 years I'll have a $300k home, while in your town I'll be worth $100k plus some gadgets".
If you can, spend your young years paying into a more expensive home, even (especially?) at some hardship to yourself. Your future self will have a substantially higher net worth in 10 years when comes time to relocate. Then you can go either to the country, or to an expensive city. But you can pretty much *never* move to the city from the country without starting another deep mortgage later in life.
My concern with this is that my favorite archiving file system venti
uses SHA-1 to generate unique block IDs for each block written to disk. This allows blocks of identical data (even though they are in different parts of the file system) to hash to the same address, making incremental storage (and backup) trivial. Currently collisions are not detected as they are expected to happen with substantially lower frequency than disk failures.
But now I suspect that my nice secure file system can be nastily compromized by generating hash-equivalent blocks. Not a huge worry, but sad to see.
Of course, the other thing about trade secrets is that employees should know when they are handling them; I don't think it takes an NDA in that case. Corporations are strong.
And it would be contract violation, which isn't criminal (neither is the trade secret stuff mind you); evidence rules are much more lenient.
Overall, I'm in agreement that Apple did this to put the fear of god into their leak, and are backing off now that that's accomplished.
Slashdot Mirror
OBLinux: They even have their own linux distro you can download: http://www.nsa.gov/selinux/
Most comp sci students have much too little exposure to real, large-scale software systems. This kind of a class is a perfect opportunity to expose them to large software. Even better, as an assignment they could read enough code to be able to make a change that doesn't break existing functionality, and hopefully adds more. It's a much harder process than most CS grads understand to change software withouth pissing off users.
Repugnicrats
In your second example, the compiler *cannot* remove the sub-expression because the case statement that gets you there crosses a basic block boundary; the return statement from the blocking code, and the jump in through the switch are caught as valid C constructs that prevent the common sub-expression optimization.
The macros as given give you a semblance of variable continuity and scoping, but the compiler, after the macro substitutions, just sees a return on the end of the blocking section, and a switch into the code following, something like:
The ugliness in the macros is about letting other control constructs live around your switch in, but still generates legit code, but, for example, you can't use a local varible as an index to your for loop. Yuck.It's ugly as sin, but your compiler had better get it right, or else it's not a C compiler.
Subtract One and Branch if Less than or EQual
The argument that Rob Pike makes in A Concurrent Window System and with Luca Cardelli in Squeak: a Language for Communicating with Mice is that many of the event systems and associated state machines that we write can be much simplified by treating input multiplexing, and thus coroutine-like structures, as language primitives.
This work follows directly from Hoare's Communicating Sequential Processes - a good summary can be found here. Working with CSP only a little has convinced me of how much easier so many systems tasks are in this framework than in the world of the massive state-system/event loop world.
Hideous, but efficiency is not it's problem.
Perhaps "non-standard" but it is standards compliant.
And dashboard! I get my stock prices at my fingertips - I'm a chronic reloader, and this is too easy. I keep clocks around for all the people I have to collaborate who are in different time zones. I keep the current weather at both ends of my commute visible (sometimes the distant weather has an effect on when I start my commute - it's right there to see in a hurry).
Way better features than I thought they were.
The space savings is huge though: the amp is hidden in a closet, and iTunes runs on an Airport Express. All other components are gone. I don't need to even have shelving for the CDs. Net savings is a wall-slot for a new book case.
Heck, PC games require the developer to be very aware of the architecture; that's how they tune for performance; consoles just tend not to look quite like a PC, and thinking of them as PCs is just asking to produce (technically) poor games.
Frankly, I'd be extatic if more PC programmers paid attention to the changes in architecture that have been happenning in the last few years: memory bandwidth is now king, much more so than processor speed. But few optimize their code for the bus...
Santa Cruz, I think you mean...Intel is in Santa Clara.
You should probably purchase a second copy of the packaged goods to install on the second machine though :-)
Hell, some of them even support pointy-clicky stuff.
It's the same question as asking if Schroedinger's cat notices if it is alive or dead. I assume it does, but that doesn't affect the outside observer.
True, but still sad. It made it nasty enough that it didn't get used enough, and did a lot to slow adoption of SIMD units :-(
Go write some VMX code and compare it to MMX - especially if you have any streaming/number crunching to do.
I was at a tallships festival where people were required to present ID before being allowed on board. Volunteers looked at the ID, nodded, and let you on. WTF?
ID does not certify someone not to be a whacked out nut job.
I got burned in the stock crash a few years ago; for reasons that aren't entirely rational I seem to trust real estate better than some other investments. And on top of, my local market has interesting constraints leading to a 10 year up-and-up...
I believe in living my life to open up options, not shut them down. The argument that city property drops in value doesn't hold: low-end city property might drop, but middle to high rarely does on the time scale we work in. Those parts of cities have died that way were industrial worker neighbourhoods destroyed by the advent of the automobile and passing of manufacturing jobs.
So again, tell me why you think high-value enforced savings plans in one's youth are wrong?
An anectode: a friend of mine was offered two faculty positions, one in a rural setting and one in a large city. The salary was a little higher in the large city. When the rural school argued "but homes here cost only $100k, but they cost $300k in the city" my friend answered: "then it's clear, I must accept the position in the city". "But why?" "Because in 20 years I'll have a $300k home, while in your town I'll be worth $100k plus some gadgets".
If you can, spend your young years paying into a more expensive home, even (especially?) at some hardship to yourself. Your future self will have a substantially higher net worth in 10 years when comes time to relocate. Then you can go either to the country, or to an expensive city. But you can pretty much *never* move to the city from the country without starting another deep mortgage later in life.
But now I suspect that my nice secure file system can be nastily compromized by generating hash-equivalent blocks. Not a huge worry, but sad to see.
Wow. US IP law is crazy. So there is basically no advantage to letting the public benefit from the invention if you keep it a secret. Madness.
And it would be contract violation, which isn't criminal (neither is the trade secret stuff mind you); evidence rules are much more lenient.
Overall, I'm in agreement that Apple did this to put the fear of god into their leak, and are backing off now that that's accomplished.