Trac #33213: use @cached_function for the spawned processes file.

This fixes an accidental change in behavior that was introduced in an
earlier commit. The path to this file shouldn't be computed when the
module is loaded -- only when it is requested. A @lazy_string would
work here, but in my opinion the added abstraction on top of the
more-familiar @cached_function is not worth it.

src/sage/interfaces/quit.py

@@ -13,10 +13,25 @@
 
 import os
 
-import atexit, tempfile
-_spd = tempfile.TemporaryDirectory()
-SAGE_SPAWNED_PROCESS_FILE = os.path.join(_spd.name, "spawned_processes")
-atexit.register(lambda: _spd.cleanup())
+from sage.misc.cachefunc import cached_function
+
+
+@cached_function
+def sage_spawned_process_file():
+    """
+    EXAMPLES::
+
+        sage: from sage.interfaces.quit import sage_spawned_process_file
+        sage: len(sage_spawned_process_file()) > 1
+        True
+
+    """
+    import atexit, tempfile
+    f = tempfile.NamedTemporaryFile(delete=False)
+    f.close()
+    atexit.register(lambda: os.remove(f.name))
+    return f.name
+
 
 def register_spawned_process(pid, cmd=''):
     """
@@ -27,7 +42,7 @@ def register_spawned_process(pid, cmd=''):
         cmd = cmd.strip().split()[0]
     # This is safe, since only this process writes to this file.
     try:
-        with open(SAGE_SPAWNED_PROCESS_FILE, 'a') as o:
+        with open(sage_spawned_process_file(), 'a') as o:
             o.write('%s %s\n'%(pid, cmd))
     except IOError:
         pass
@@ -88,9 +103,7 @@ def kill_spawned_jobs(verbose=False):
 
         sage: sage.interfaces.quit.expect_quitall()
     """
-    if not os.path.exists(SAGE_SPAWNED_PROCESS_FILE):
-        return
-    with open(SAGE_SPAWNED_PROCESS_FILE) as f:
+    with open(sage_spawned_process_file()) as f:
         for L in f:
             i = L.find(' ')
             pid = L[:i].strip()