PEP: | 651 |
---|---|
Title: | Robust Stack Overflow Handling |
Author: | Mark Shannon |
Status: | Rejected |
Type: | Standards Track |
Created: | 18-Jan-2021 |
Post-History: | 19-Jan-2021 |
Another advantage here is that if recursion happens even somewhere in native code, it will also be caught and proper Java dump stack produced, as opposed to Mac OS X CrashReporter popping up. The initial feedback from the Runtime team, however, is that we used to use alternate stack, but we took it out because it was not robust - needs discussion. Course Information Overview. CS 2112/ENGRD 2112 is an honors version of CS 2110/ENGRD 2110.Credit is given for only one of 2110 and 2112. Transfer between 2110 and 2112 (in either direction) is encouraged during the first three weeks. As David mentioned, OS X is missing the handy -a option that gnu cp has. However, if you use -R to do a recursive copy, then it will copy symlinks by default, so. Cp -R source destination ought to work.
Contents
- Specification
- C-API
- Implementation
Does not seem to be an option (using Mac OS X 10.10.3). – pdeli Apr 15 '15 at 11:04. Add a comment 2 Answers Active Oldest Votes. In order to successfully copy the files in the first place, you need at least have read access to the files at the original location. To make sure that you can. Recursion: Graph recursive functions by defining f(0)=C and defining f(n) based on f(n-1). On a mission to transform learning through computational thinking, Shodor is dedicated to the reform and improvement of mathematics and science education through student enrichment, faculty enhancement, and interactive curriculum development at all levels.
This PEP has been rejected by the Python Steering Council.
This PEP proposes that Python should treat machine stack overflow differently from runaway recursion.
This would allow programs to set the maximum recursion depth to fit their needsand provide additional safety guarantees.
If this PEP is accepted, then the following program will run safely to completion:
and the following program will raise a StackOverflow, without causing a VM crash:
https://trueefiles817.weebly.com/goetia-1-2-download-free.html. CPython uses a single recursion depth counter to prevent both runaway recursion and C stack overflow.However, runaway recursion and machine stack overflow are two different things.Allowing machine stack overflow is a potential security vulnerability, but limiting recursion depth can prevent theuse of some algorithms in Python.
Currently, if a program needs to deeply recurse it must manage the maximum recursion depth allowed,hopefully managing to set it in the region between the minimum needed to run correctly and the maximum that is safeto avoid a memory protection error.
By separating the checks for C stack overflow from checks for recursion depth,pure Python programs can run safely, using whatever level of recursion they require.
CPython currently relies on a single limit to guard against potentially dangerous stack overflowin the virtual machine and to guard against run away recursion in the Python program.
This is a consequence of the implementation which couples the C and Python call stacks.By breaking this coupling, we can improve both the usability of CPython and its safety.
The recursion limit exists to protect against runaway recursion, the integrity of the virtual machine should not depend on it.Similarly, recursion should not be limited by implementation details.
Two new exception classes will be added, StackOverflow and RecursionOverflow, both of which will besub-classes of RecursionError
StackOverflow exception
A StackOverflow exception will be raised whenever the interpreter or builtin module codedetermines that the C stack is at or nearing a limit of safety.StackOverflow is a sub-class of RecursionError,so any code that handles RecursionError will handle StackOverflow
RecursionOverflow exception
A RecursionOverflow exception will be raised when a call to a Python functioncauses the recursion limit to be exceeded.This is a slight change from current behavior which raises a RecursionError.RecursionOverflow is a sub-class of RecursionError,so any code that handles RecursionError will continue to work as before.
Decoupling the Python stack from the C stack
In order to provide the above guarantees and ensure that any program that worked previouslycontinues to do so, the Python and C stack will need to be separated.That is, calls to Python functions from Python functions, should not consume space on the C stack.Calls to and from builtin functions will continue to consume space on the C stack.
Cricut craft room software download. The size of the C stack will be implementation defined, and may vary from machine to machine.It may even differ between threads. However, there is an expectation that any code that could runwith the recursion limit set to the previous default value, will continue to run.
Many operations in Python perform some sort of call at the C level.Most of these will continue to consume C stack, and will result in aStackOverflow exception if uncontrolled recursion occurs.
Other Implementations
Other implementations are required to fail safely regardless of what value the recursion limit is set to.
If the implementation couples the Python stack to the underlying VM or hardware stack,then it should raise a RecursionOverflow exception when the recursion limit is exceeded,but the underlying stack does not overflow.If the underlying stack overflows, or is near to overflow,then a StackOverflow exception should be raised.
C-API
A new function, Py_CheckStackDepth() will be added, and the behavior of Py_EnterRecursiveCall() will be modified slightly.
Py_CheckStackDepth()
int Py_CheckStackDepth(const char *where)will return 0 if there is no immediate danger of C stack overflow.It will return -1 and set an exception, if the C stack is near to overflowing.The where parameter is used in the exception message, in the same fashionas the where parameter of Py_EnterRecursiveCall().
Py_EnterRecursiveCall()
Py_EnterRecursiveCall() will be modified to call Py_CheckStackDepth() before performing its current function.
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PyLeaveRecursiveCall()
Py_LeaveRecursiveCall() will remain unchanged.
This feature is fully backwards compatibile at the Python level.Some low-level tools, such as machine-code debuggers, will need to be modified.For example, the gdb scripts for Python will need to be aware that there may be more than one Python frameper C frame.
C code that uses the Py_EnterRecursiveCall(), PyLeaveRecursiveCall() pair offunctions will continue to work correctly. In addition, Py_EnterRecursiveCall()may raise a StackOverflow exception.
New code should use the Py_CheckStackDepth() function, unless the code wants tocount as a Python function call with regard to the recursion limit.
We recommend that 'python-like' code, such as Cython-generated functions,use Py_EnterRecursiveCall(), but other code use Py_CheckStackDepth().
It will no longer be possible to crash the CPython virtual machine through recursion.
It is unlikely that the performance impact will be significant.
The additional logic required will probably have a very small negative impact on performance.The improved locality of reference from reduced C stack use should have some small positive impact.
It is hard to predict whether the overall effect will be positive or negative,but it is quite likely that the net effect will be too small to be measured.
Monitoring C stack consumption
Gauging whether a C stack overflow is imminent is difficult. So we need to be conservative.We need to determine a safe bounds for the stack, which is not something possible in portable C code.
For major platforms, the platform specific API will be used to provide an accurate stack bounds.However, for minor platforms some amount of guessing may be required.While this might sound bad, it is no worse than the current situation, where we guess that thesize of the C stack is at least 1000 times the stack space required for the chain of calls from_PyEval_EvalFrameDefault to _PyEval_EvalFrameDefault.
This means that in some cases the amount of recursion possible may be reduced.In general, however, the amount of recursion possible should be increased, as many calls will use no C stack. Robocop games for free.
Our general approach to determining a limit for the C stack is to get an address within the current C frame,as early as possible in the call chain. The limit can then be guessed by adding some constant to that.
Making Python-to-Python calls without consuming the C stack
Calls in the interpreter are handled by the CALL_FUNCTION,CALL_FUNCTION_KW, CALL_FUNCTION_EX and CALL_METHOD instructions.The code for those instructions will be modified so that whena Python function or method is called, instead of making a call in C,the interpreter will setup the callee's frame and continue interpretation as normal.
The RETURN_VALUE instruction will perform the reverse operation,except when the current frame is the entry frame of the interpreterwhen it will return as normal.
None, as yet.
This document is placed in the public domain or under theCC0-1.0-Universal license, whichever is more permissive.
Source: https://github.com/python/peps/blob/master/pep-0651.rstStart up from macOS Recovery
Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:
Apple silicon
Turn on your Mac and continue to press and hold the power button until you see the startup options window. Click the gear icon labeled Options, then click Continue.
Intel processor
Make sure that your Mac has a connection to the internet. Then turn on your Mac and immediately press and hold Command (⌘)-R until you see an Apple logo or other image.
If you're asked to select a user you know the password for, select the user, click Next, then enter their administrator password. Optric mac os.
Reinstall macOS
Select Reinstall macOS from the utilities window in macOS Recovery, then click Continue and follow the onscreen instructions.
Follow these guidelines during installation:
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- If the installer asks to unlock your disk, enter the password you use to log in to your Mac.
- If the installer doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk first.
- If the installer offers you the choice between installing on Macintosh HD or Macintosh HD - Data, choose Macintosh HD.
- Allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart and show a progress bar several times, and the screen might be empty for minutes at a time.
After installation is complete, your Mac might restart to a setup assistant. If you're selling, trading in, or giving away your Mac, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup.
Other macOS installation options
When you install macOS from Recovery, you get the current version of the most recently installed macOS, with some exceptions:
- On an Intel-based Mac: If you use Shift-Option-Command-R during startup, you're offered the macOS that came with your Mac, or the closest version still available. If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac. Otherwise you're offered the macOS that came with your Mac, or the closest version still available.
- If the Mac logic board was just replaced, you may be offered only the latest macOS that is compatible with your Mac. If you just erased your entire startup disk, you may be offered only the macOS that came with your Mac, or the closest version still available.
You can also use these methods to install macOS, if the macOS is compatible with your Mac:
- Use the App Store to download and install the latest macOS.
- Use the App Store or a web browser to download and install an earlier macOS.
- Use a USB flash drive or other secondary volume to create a bootable installer.