fix: use rayon::current_num_threads() for multithreaded zstd encode

Cargo.toml

@@ -10,11 +10,12 @@ license = "AGPL-3.0-or-later"
 
 [dependencies]
 bincode = { version = "2.0.0-rc.3", optional = true }
-once_cell = "1.17.1"
-rayon = { version = "1.7.0", optional = true }
-regex = "1.8.1"
-zstd = { version = "0.12.3", optional = true, features = ["zstdmt"] }
+once_cell = "1.18.0"
+rayon = { version = "1.8.0", optional = true }
+regex = "1.9.5"
+zstd = { version = "0.12.4", optional = true, default-features = false }
 
 [features]
 default = ["bincode", "rayon"]
 custom-alloc = []
+rayon = ["dep:rayon", "zstd?/zstdmt"]

src/file.rs

@@ -16,7 +16,6 @@ use bincode::{Decode, Encode};
 use std::fs::File;
 use std::io::{BufReader, BufWriter, Read, Write};
 use std::path::Path;
-use std::thread::available_parallelism;
 
 const MAGIC: u32 = 0x09f15790;
 const VERSION: u8 = 1;
@@ -88,12 +87,11 @@ pub fn save_data_into_std_write<T: FileData, W: Write>(
     if let Some(compression_level) = compression_level {
         let mut zstd_encoder = zstd::stream::Encoder::new(writer, compression_level)
             .map_err(|e| format!("Failed to create zstd encoder: {}", e))?;
-        let workers = available_parallelism()
-            .map_err(|e| format!("Failed to get cpu cores: {}", e))?
-            .get() as u32;
+
+        #[cfg(feature = "rayon")]
         zstd_encoder
-            .multithread(workers)
-            .map_err(|e| format!("Failed to enable multithreaded compression: {}", e))?;
+            .multithread(rayon::current_num_threads() as u32)
+            .map_err(|e| format!("Failed to enable multithreaded zstd encoder: {}", e))?;
 
         encode_into_std_write(data, &mut zstd_encoder, "Failed to write data")?;
         zstd_encoder