Add a test case for jemallocator as the global allocator

Author: tatsuya6502

tests/test_jemallocator.rs

@@ -0,0 +1,65 @@
+// -*- coding:utf-8-unix -*-
+
+use jemalloc_ctl;
+use jemallocator;
+
+#[global_allocator]
+static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
+
+type UnitResult = Result<(), Box<dyn std::error::Error>>;
+
+fn main() -> UnitResult {
+    do_allocate_heap()
+}
+
+#[test]
+fn test_jemallocator() -> UnitResult {
+    do_allocate_heap()
+}
+
+fn do_allocate_heap() -> UnitResult {
+    use jemalloc_ctl::{epoch, stats};
+    use rand::prelude::*;
+
+    const SIZE: usize = 100000;
+
+    let mut rng = SmallRng::from_rng(thread_rng())?;
+
+    let v = rng
+        .sample_iter(&rand::distributions::Standard)
+        .take(SIZE)
+        .collect::<Vec<usize>>();
+    let v_byte_size = v.len() * std::mem::size_of::<usize>();
+
+    // many statistics are cached and only updated when the epoch is advanced.
+    epoch::advance().map_err(stringify)?;
+    let allocated = stats::allocated::read().map_err(stringify)?;
+    let resident = stats::resident::read().map_err(stringify)?;
+    println!(
+        "{} bytes used by a Vec<uzize> with len {}.",
+        v_byte_size,
+        v.len()
+    );
+    println!(
+        "{} bytes allocated/{} bytes resident using jemalloc",
+        allocated, resident
+    );
+
+    assert!(
+        allocated >= v_byte_size,
+        "allocated size ({} bytes) is smaller than the vector size ({} bytes).",
+        allocated,
+        v_byte_size,
+    );
+
+    // to prevent the compiler to optimize the vec out, read its value at
+    // a random location.
+    let i = rng.gen_range(0, SIZE);
+    println!("v[{}] = {}", i, v[i]);
+
+    Ok(())
+}
+
+fn stringify(x: impl ToString) -> String {
+    x.to_string()
+}