Removed usage of num_cpus (#2387)

* Removed usage of num_cpus
* handling error

Cargo.toml

@@ -30,7 +30,6 @@ tempfile = { version = "3.3.0", optional = true }
 log = "0.4.16"
 serde = { version = "1.0.136", features = ["derive"] }
 serde_json = "1.0.79"
-num_cpus = "1.13.1"
 fs4 = { version = "0.8.0", optional = true }
 levenshtein_automata = "0.2.1"
 uuid = { version = "1.0.0", features = ["v4", "serde"] }
@@ -117,7 +116,7 @@ unstable = [] # useful for benches.
 
 quickwit = ["sstable", "futures-util"]
 
-# Compares only the hash of a string when indexing data. 
+# Compares only the hash of a string when indexing data.
 # Increases indexing speed, but may lead to extremely rare missing terms, when there's a hash collision.
 # Uses 64bit ahash.
 compare_hash_only = ["stacker/compare_hash_only"]

src/index/index.rs

@@ -4,6 +4,7 @@ use std::fmt;
 use std::path::Path;
 use std::path::PathBuf;
 use std::sync::Arc;
+use std::thread::available_parallelism;
 
 use super::segment::Segment;
 use super::segment_reader::merge_field_meta_data;
@@ -340,7 +341,7 @@ impl Index {
     /// Replace the default single thread search executor pool
     /// by a thread pool with as many threads as there are CPUs on the system.
     pub fn set_default_multithread_executor(&mut self) -> crate::Result<()> {
-        let default_num_threads = num_cpus::get();
+        let default_num_threads = available_parallelism()?.get();
         self.set_multithread_executor(default_num_threads)
     }
 
@@ -621,7 +622,7 @@ impl Index {
         &self,
         memory_budget_in_bytes: usize,
     ) -> crate::Result<IndexWriter<D>> {
-        let mut num_threads = std::cmp::min(num_cpus::get(), MAX_NUM_THREAD);
+        let mut num_threads = std::cmp::min(available_parallelism()?.get(), MAX_NUM_THREAD);
         let memory_budget_num_bytes_per_thread = memory_budget_in_bytes / num_threads;
         if memory_budget_num_bytes_per_thread < MEMORY_BUDGET_NUM_BYTES_MIN {
             num_threads = (memory_budget_in_bytes / MEMORY_BUDGET_NUM_BYTES_MIN).max(1);