PersistentShell polling causes excessive CPU on WSL

Fixes on record

Merged to main. A stamp counts the issues a fix is linked to.

• #2996 fix(shell): exponential backoff for persistent shell polling

  merged to main

  files: tools/environments/persistent_shell.py, tools/environments/ssh.py

  Show the diff

  • tools/environments/persistent_shell.py

    @@ -40,7 +40,8 @@ def _execute_oneshot(self, command: str, cwd: str, *,
         def _cleanup_temp_files(self): ...
     
         _session_id: str = ""
    -    _poll_interval: float = 0.01
    +    _poll_interval_start: float = 0.01  # initial poll interval (10ms)
    +    _poll_interval_max: float = 0.25    # max poll interval (250ms) — reduces I/O for long commands
     
         @property
         def _temp_prefix(self) -> str:
    @@ -224,7 +225,7 @@ def _execute_persistent_locked(self, command: str, cwd: str,
             )
             self._send_to_shell(ipc_script)
             deadline = time.monotonic() + timeout
    -        poll_interval = self._poll_interval
    +        poll_interval = self._poll_interval_start  # starts at 10ms, backs off to 250ms
     
             while True:
                 if is_interrupted():
    @@ -256,6 +257,10 @@ def _execute_persistent_locked(self, command: str, cwd: str,
                     break
     
                 time.sleep(poll_interval)
    +            # Exponential backoff: fast start (10ms) for quick commands,
    +            # ramps up to 250ms for long-running commands — reduces I/O by 10-25x
    +            # on WSL2 where polling keeps the VM hot and memory pressure high.
    +            poll_interval = min(poll_interval * 1.5, self._poll_interval_max)
     
             output, exit_code, new_cwd = self._read_persistent_output()
             if new_cwd:

  • tools/environments/ssh.py

    @@ -87,7 +87,7 @@ def _establish_connection(self):
             except subprocess.TimeoutExpired:
                 raise RuntimeError(f"SSH connection to {self.user}@{self.host} timed out")
     
    -    _poll_interval: float = 0.15
    +    _poll_interval_start: float = 0.15  # SSH: higher initial interval (150ms) for network latency
     
         @property
         def _temp_prefix(self) -> str: