adjust threshold

Signed-off-by: Yilin Chen <sticnarf@gmail.com>

Author: sticnarf

src/pool/spawn.rs

@@ -89,7 +89,8 @@ impl WorkersInfo for u64 {
     }
 }
 
-const BACKUP_THRESHOLD: i64 = 64;
+const BACKUP_TO_ACTIVE_THRESHOLD: i64 = -16;
+const ACTIVE_TO_BACKUP_THRESHOLD: i64 = 128;
 
 /// The core of queues.
 ///
@@ -135,7 +136,7 @@ impl<T> QueueCore<T> {
                     self.backup_count.store(0, Ordering::SeqCst);
                 } else {
                     backup_count = self.backup_count.fetch_sub(1, Ordering::SeqCst) - 1;
-                    while backup_count < -BACKUP_THRESHOLD {
+                    while backup_count < BACKUP_TO_ACTIVE_THRESHOLD {
                         match self.backup_count.compare_exchange_weak(
                             backup_count,
                             0,
@@ -180,7 +181,7 @@ impl<T> QueueCore<T> {
     pub fn park_to_backup(&self) -> bool {
         let mut v = self.backup_count.load(Ordering::SeqCst);
         loop {
-            if v < BACKUP_THRESHOLD {
+            if v < ACTIVE_TO_BACKUP_THRESHOLD {
                 return false;
             }
             match self