system | A component system syntax for CSS
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A component system syntax for CSS
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QUESTION
I am writing my project and wondered. When I read literature or watch videos, I see that this is bad practice. Why? Is this bad for the system?
What is the difference between this
...ANSWER
Answered 2021-Jun-16 at 00:17You have to initialize all instance properties somehow. And you have to do it right up front, either in the declaration line or in your init method.
But what if you don't actually have the initial value until later, like in viewDidLoad? Then it is silly to supply a real heavyweight value only to replace it later:
QUESTION
I am trying to configure github webhooks with my jenkins server but I keep getting "failed to connect". Note that I am using a public ip and not a private or localhost address, At first, icmp protocol was blocked on my firewall but even after allowing it, it still doesn't work.
However, when I proxy my server (using smee client) and use the proxied url in the webhook instead, it works fine, so I thought the problem was jenkins url (in system configuration of jenkins) so I changed that to the public ip but it doesn't have any effect, now I'm clueless.
It might be relevant to mention that jenkins is running on a docker container,
...ANSWER
Answered 2021-Jun-15 at 23:51Apparently the webhook must pass through a web server and not to jenkins directly, So I configured nginx as a reverse proxy to jenkins server and it worked fine.
QUESTION
I understand that after calling fork() the child process inherits the per-process file descriptor table of its parent (pointing to the same system-wide open file tables). Hence, when opening a file in a parent process and then calling fork(), both the child and parent can write to that file without overwriting one another's output (due to a shared offset in the open-file table entry).
However, suppose that, we call open() on some file after a fork (in both the parent and the child). Will this create a separate entries in the system-wide open file table, with a separate set of offsets and read-write permission flags for the child (despite the fact that it's technically the same file)? I've tried looking this up and I don't seem to be able to find a clear answer.
I'm asking this mainly since I was playing around with writing to files, and it seems like only one the outputs of the parent and child ends up in the file in the aforementioned situation. This seemed to imply that there are separate entries in the open file table for the two separate open calls, and hence separate offsets, so the slower process overwrites the output of the other process.
To illustrate this, consider the following code:
...ANSWER
Answered 2021-May-03 at 20:22There is a difference between a file and a file descriptor (FD).
All processes share the same files. They don't necessarily have access to the same files, and a file is not its name, either; two different processes which open the same name might not actually open the same file, for example if the first file were renamed or unlinked and a new file were associated with the name. But if they do open the same file, it's necessarily shared, and changes will be mutually visible.
But a file descriptor is not a file. It refers to a file (not a filename, see above), but it also contains other information, including a file position used for and updated by calls to read and write. (You can use "positioned" read and write, pread and pwrite, if you don't want to use the position in the FD.) File descriptors are shared between parent and child processes, and so the file position in the FD is also shared.
Another thing stored in the file descriptor (in the kernel, where user processes can't get at it) is the list of permitted actions (on Unix, read, write, and/or execute, and possibly others). Permissions are stored in the file directory, not in the file itself, and the requested permissions are copied into the file descriptor when the file is opened (if the permissions are available.) It's possible for a child process to have a different user or group than the parent, particularly if the parent is started with augmented permissions but drops them before spawning the child. A file descriptor for a file opened in this manner still has the same permissions uf it is shared with a child, even if the child would itself be able to open the file.
QUESTION
In part of my application I have an option that displays a list of albums by the current artist that aren't in the music library. To get this I call a music API to get the list of all albums by that artist and then I remove the albums that are in the current library.
To cope with the different casing of names and the possibility of missing (or extra punctuation) in the title I have written an IEqualityComparer to use in the .Except call:
ANSWER
Answered 2021-Jun-15 at 23:05If you're going to use the CompareOptions enum, I feel like you might as well use it with the CompareInfo class that it's documented as being designed for:
Defines the string comparison options to use with CompareInfo.
Then you can just use the GetHashCode(string, CompareOptions) method from that class (and even the Compare(string, string, CompareOptions) method if you like).
QUESTION
I'm trying to create a Windows form via Powershell and I need to capture the file path and store it in a variable. After the user clicks the 'Select' button and chooses the file, I would like to store the file path in a variable. Can someone please help me with this? The part of the code that shows the file path is the $selectButton.Add_Click() method.
...ANSWER
Answered 2021-Jun-15 at 21:22Following your .ShowDialog() call, you can simply query the value of your $pathTextBox text-box object.
QUESTION
I have file txt with format like this
...ANSWER
Answered 2021-Jun-15 at 21:31You add each line to the variable list_Siswa. So for instance the first element of list_Siswa will be ["Nama"," John"], and so data_Siswa[0] equals "Nama" and data_Siswa[1] equals " John". Then data_Siswa[2] throws an error, because there is no such element in the array.
The code isn't smart enough to see Nama: John and assume the following lines are grades that should be associated with John. If you want that, you'll have to do it yourself.
QUESTION
Or, more specifically, does it use the default shell, or actually running the actual file. Example: system("echo Hello, World!"). Would this run using, lets say Bash, or would this run by telling to kernal to run a command? Also, is this on topic, or would this fit better somewhere else?
ANSWER
Answered 2021-Jun-15 at 21:28man system is your friend here. This is what is says on my system:
The system() library function uses fork(2) to create a child process that executes the shell command specified in command using execl(3) as follows:
QUESTION
Hey guys given the example below in C when operating on a 64bit system as i understand, a pointer is 8 byte. Wouldn't the calloc here allocate too little memory as it takes the sizeof(int) which is 4 bytes? Thing is, this still works. Does it overwrite the memory? Would love some clarity on this.
Bonus question: if i remove the type casting (int*) i sometimes get a warning "invalid conversion from 'void*' to 'int*', does this mean it still works considering the warning?
...ANSWER
Answered 2021-Jun-15 at 21:19calloc is allocating the amount of memory you asked for on the heap. The pointer is allocated by your compiler either in registers or on the stack. In this case, calloc is actually allocating enough memory for 4 ints on the heap (which on most systems is going to be 16 bytes, but for the arduino uno it would be 8 because the sizeof(int) is 2), then storing the pointer to that allocated memory in your register/stack location.
For the bonus question: Arduino uses C++ instead of C, and that means that it uses C++'s stronger type system. void * and int * are different types, so it's complaining. You should cast the return value of malloc when using C++.
QUESTION
I'm trying to help a developer who is trying to harden a web server against server-side request forgery. In short, I've wrote a script that sends a "forged" HTTP request which we will use to test against the server until it is configured to not respond to such manipulated requests. I'm getting an error on Invoke-WebRequest: "Cannot validate argument on parameter 'Uri'" and while I've tried a ton of different combos of the below code I cannot get it to fly. Any thoughts? (Note: my-ef.example.com below is not the actual host)
...ANSWER
Answered 2021-Jun-15 at 21:03$url is never specified in your code. Did you mean to run this?
QUESTION
In C++20, we got the capability to sleep on atomic variables, waiting for their value to change.
We do so by using the std::atomic::wait method.
Unfortunately, while wait has been standardized, wait_for and wait_until are not. Meaning that we cannot sleep on an atomic variable with a timeout.
Sleeping on an atomic variable is anyway implemented behind the scenes with WaitOnAddress on Windows and the futex system call on Linux.
Working around the above problem (no way to sleep on an atomic variable with a timeout), I could pass the memory address of an std::atomic to WaitOnAddress on Windows and it will (kinda) work with no UB, as the function gets void* as a parameter, and it's valid to cast std::atomic to void*
On Linux, it is unclear whether it's ok to mix std::atomic with futex. futex gets either a uint32_t* or a int32_t* (depending which manual you read), and casting std::atomic to u/int* is UB. On the other hand, the manual says
The uaddr argument points to the futex word. On all platforms, futexes are four-byte integers that must be aligned on a four- byte boundary. The operation to perform on the futex is specified in the futex_op argument; val is a value whose meaning and purpose depends on futex_op.
Hinting that alignas(4) std::atomic should work, and it doesn't matter which integer type is it is as long as the type has the size of 4 bytes and the alignment of 4.
Also, I have seen many places where this trick of combining atomics and futexes is implemented, including boost and TBB.
So what is the best way to sleep on an atomic variable with a timeout in a non UB way? Do we have to implement our own atomic class with OS primitives to achieve it correctly?
(Solutions like mixing atomics and condition variables exist, but sub-optimal)
...ANSWER
Answered 2021-Jun-15 at 20:48You shouldn't necessarily have to implement a full custom atomic API, it should actually be safe to simply pull out a pointer to the underlying data from the atomic and pass it to the system.
Since std::atomic does not offer some equivalent of native_handle like other synchronization primitives offer, you're going to be stuck doing some implementation-specific hacks to try to get it to interface with the native API.
For the most part, it's reasonably safe to assume that first member of these types in implementations will be the same as the T type -- at least for integral values [1]. This is an assurance that will make it possible to extract out this value.
... and casting
std::atomictou/int*is UB
This isn't actually the case.
std::atomic is guaranteed by the standard to be Standard-Layout Type. One helpful but often esoteric properties of standard layout types is that it is safe to reinterpret_cast a T to a value or reference of the first sub-object (e.g. the first member of the std::atomic).
As long as we can guarantee that the std::atomic contains only the u/int as a member (or at least, as its first member), then it's completely safe to extract out the type in this manner:
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