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read sample files from dedicated threads

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Reading from the mmap()ed region in the tokio threads could cause
them to stall:

*   That could affect UI serving when there were concurrent
    UI requests (i.e., not just requests that needed the reads in
    question anyway).
*   If there's a faulty disk, it could cause the UI to totally hang.
    Better to not mix disks between threads.
*   Soon, I want to handle RTSP from the tokio threads (#37). Similarly,
    we don't want RTSP streaming to block on operations from unrelated
    disks.

I went with just one thread per disk which I think is sufficient.
But it'd be possible to do a fixed-size pool instead which might improve
latency when some pages are already cached.

I also dropped the memmap dependency. I had to compute the page
alignment anyway to get mremap to work, and Moonfire NVR already is
Unix-specific, so there wasn't much value from the memmap or memmap2
crates.

Fixes #88
This commit is contained in:
Scott Lamb
2021-06-04 19:17:32 -07:00
parent 90dd68ee7c
commit 23d77693de
8 changed files with 432 additions and 50 deletions
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17
guide/troubleshooting.md
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@@ -85,12 +85,17 @@ Moonfire NVR names a few important thread types as follows:
* `main`: during `moonfire-nvr run`, the main thread does initial setup then
just waits for the other threads. In other subcommands, it does everything.
* `s-CAMERA-TYPE`: there is one of these threads for every recorded stream
(up to two per camera, where `TYPE` is `main` or `sub`). These threads read
frames from the cameras via RTSP and write them to disk.
* `sync-PATH`: there is one of these threads for every sample file directory.
These threads call `fsync` to commit sample files to disk, delete old sample
files, and flush the database.
* `s-CAMERA-TYPE` (one per stream, where `TYPE` is `main` or `sub`):
These threads read frames from the cameras via RTSP and write them to disk.
* `sync-PATH` (one per sample file directory): These threads call `fsync` to
* commit sample files to disk, delete old sample files, and flush the
database.
* `r-PATH` (one per sample file directory): These threads read sample files
from disk for serving `.mp4` files.
* `tokio-runtime-worker` (one per core): these threads handle HTTP requests.
* `logger`: this thread writes the log buffer to `stderr`. Logging is
asynchronous; other threads don't wait for log messages to be written
unless the log buffer is full.
You can use the following command to teach [`lnav`](http://lnav.org/) Moonfire
NVR's log format: