Re: Disk write in a "for" loop with RwMutex never happens
On 30/08/2022 8:16 AM, Gavin Ray wrote: It must have been the "writing at end of file" bit? I don't know. It read like it should work. The offsets were correct, it just didn't work *shrug*.
Re: Disk write in a "for" loop with RwMutex never happens
On Monday, 29 August 2022 at 15:52:31 UTC, rikki cattermole wrote: After a bunch of playing around I managed to determine that it is as simple as the mode. exists(dbFileName) ? "r+" : "w+" Will fix it. Of course you shouldn't delete the file like that method is doing. It should probably reinitialize the FILE* descriptor. D'oh! I didn't even think about the mode: > `a+ or ab+ or a+b` > "Append; open or create file for update, writing at end-of-file." It must have been the "writing at end of file" bit? Thanks Rikki. /embarrassed
Re: Disk write in a "for" loop with RwMutex never happens
On Monday, 29 August 2022 at 16:21:53 UTC, ag0aep6g wrote: You never change `pageId`. So as far as I can tell, you're always `seek`-ing to the same position, and you just overwrite the same piece of the file again and again. Whoops. I guess I missed the point of the question there.
Re: Disk write in a "for" loop with RwMutex never happens
On Sunday, 28 August 2022 at 22:46:17 UTC, Gavin Ray wrote:
I've put the code, stripped to a minimal example here:
- https://ldc.godbolt.org/z/fzsx3Tnnn
[...]
But if the same code is placed inside of a `for` loop, suddenly
no writes occur:
[...]
Does anyone know what is happening here? It's really puzzling.
Relevant pieces of the code:
```d
class DiskManager
{
void writePage(PageId pageId, ubyte[PAGE_SIZE] pageData)
{
synchronized (dbIOMutex.writer)
{
dbFile.seek(pageId * PAGE_SIZE);
dbFile.rawWrite(pageData);
}
}
}
void singleReadWrite()
{
PageId pageId = 0;
diskManager.writePage(pageId, pageData);
}
void multiReadWrite()
{
PageId pageId = 0;
foreach (i; 0 .. 10)
{
diskManager.writePage(pageId, pageData);
}
}
```
You never change `pageId`. So as far as I can tell, you're always
`seek`-ing to the same position, and you just overwrite the same
piece of the file again and again.
Re: Disk write in a "for" loop with RwMutex never happens
After a bunch of playing around I managed to determine that it is as simple as the mode. exists(dbFileName) ? "r+" : "w+" Will fix it. Of course you shouldn't delete the file like that method is doing. It should probably reinitialize the FILE* descriptor.
Re: Disk write in a "for" loop with RwMutex never happens
On Monday, 29 August 2022 at 07:04:49 UTC, bauss wrote:
Does anyone know what is happening here? It's really puzzling.
You probably need to flush the output.
That's a good idea. I gave it a shot, and the following doesn't
seem to change anything unfortunately:
```d
void writePage(PageId pageId, ubyte[PAGE_SIZE] pageData)
{
synchronized (dbIOMutex.writer)
{
dbFile.seek(pageId * PAGE_SIZE);
dbFile.rawWrite(pageData);
dbFile.flush();
dbFile.sync();
}
}
```
Re: Disk write in a "for" loop with RwMutex never happens
On Sunday, 28 August 2022 at 22:46:17 UTC, Gavin Ray wrote: I've put the code, stripped to a minimal example here: - https://ldc.godbolt.org/z/fzsx3Tnnn You can see that the single write + read version of the code works just fine: ``` pageData[0..4] = [1, 2, 3, 4] readData[0..4] = [1, 2, 3, 4] ``` Where here, `pageData` is the data to be written to a file, and `readData` is the result of trying to read the freshly written file data. But if the same code is placed inside of a `for` loop, suddenly no writes occur: ```d pageData[0..4] = [0, 0, 0, 0] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 1] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 2] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 3] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 4] readData[0..4] = [0, 0, 0, 0] // ... ``` Does anyone know what is happening here? It's really puzzling. You probably need to flush the output.
Disk write in a "for" loop with RwMutex never happens
I've put the code, stripped to a minimal example here: - https://ldc.godbolt.org/z/fzsx3Tnnn You can see that the single write + read version of the code works just fine: ``` pageData[0..4] = [1, 2, 3, 4] readData[0..4] = [1, 2, 3, 4] ``` Where here, `pageData` is the data to be written to a file, and `readData` is the result of trying to read the freshly written file data. But if the same code is placed inside of a `for` loop, suddenly no writes occur: ```d pageData[0..4] = [0, 0, 0, 0] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 1] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 2] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 3] readData[0..4] = [0, 0, 0, 0] pageData[0..4] = [0, 0, 0, 4] readData[0..4] = [0, 0, 0, 0] // ... ``` Does anyone know what is happening here? It's really puzzling.
