Move env.{add,get}_lock() into cycles.py, and rename.

They really aren't locks at all, they're a cycle detector.  Also rename
REDO_LOCKS to a more meaningful REDO_CYCLES.  And we'll move the
CyclicDependencyError exception in here as well, instead of state.py
where it doesn't really belong.

redo/builder.py

@@ -1,5 +1,5 @@
 import sys, os, errno, stat, signal, time
-import env, jobserver, state, paths
+import cycles, env, jobserver, state, paths
 from helpers import unlink, close_on_exec
 import logs
 from logs import debug2, err, warn, meta, check_tty
@@ -129,7 +129,7 @@ class BuildJob(object):
         try:
             try:
                 is_target, dirty = self.shouldbuildfunc(self.t)
-            except state.CyclicDependencyError:
+            except cycles.CyclicDependencyError:
                 err('cyclic dependency while checking %s\n' % _nice(self.t))
                 raise ImmediateReturn(208)
             if not dirty:
@@ -264,7 +264,7 @@ class BuildJob(object):
         os.environ['REDO_PWD'] = state.relpath(newp, env.STARTDIR)
         os.environ['REDO_TARGET'] = self.basename + self.ext
         os.environ['REDO_DEPTH'] = env.DEPTH + '  '
-        env.add_lock(str(self.lock.fid))
+        cycles.add(self.lock.fid)
         if dn:
             os.chdir(dn)
         os.dup2(self.f.fileno(), 1)
@@ -499,7 +499,7 @@ def main(targets, shouldbuildfunc):
                 meta('waiting', state.target_relpath(t))
                 try:
                     lock.check()
-                except state.CyclicDependencyError:
+                except cycles.CyclicDependencyError:
                     err('cyclic dependency while building %s\n' % _nice(t))
                     retcode[0] = 208
                     return retcode[0]

redo/cycles.py

@@ -0,0 +1,24 @@
+"""Code for detecting and aborting on cyclic dependency loops."""
+import os
+
+
+class CyclicDependencyError(Exception):
+    pass
+
+
+def _get():
+    """Get the list of held cycle items."""
+    return os.environ.get('REDO_CYCLES', '').split(':')
+
+
+def add(fid):
+    """Add a lock to the list of held cycle items."""
+    items = set(_get())
+    items.add(str(fid))
+    os.environ['REDO_CYCLES'] = ':'.join(list(items))
+
+
+def check(fid):
+    if str(fid) in _get():
+        # Lock already held by parent: cyclic dependency
+        raise CyclicDependencyError()

redo/deps.py

@@ -1,5 +1,5 @@
 import os
-import env, state
+import cycles, env, state
 from logs import debug
 
 CLEAN = 0
@@ -11,7 +11,7 @@ def isdirty(f, depth, max_changed,
             set_checked=state.File.set_checked_save,
             log_override=state.warn_override):
     if f.id in already_checked:
-        raise state.CyclicDependencyError()
+        raise cycles.CyclicDependencyError()
     # make a copy of the list, so upon returning, our parent's copy
     # is unaffected
     already_checked = list(already_checked) + [f.id]

redo/env.py

@@ -33,14 +33,3 @@ os.environ['REDO_UNLOCKED'] = ''  # not inheritable by subprocesses
 
 NO_OOB = os.environ.get('REDO_NO_OOB', '') and 1 or 0
 os.environ['REDO_NO_OOB'] = ''    # not inheritable by subprocesses
-
-
-def get_locks():
-    """Get the list of held locks."""
-    return os.environ.get('REDO_LOCKS', '').split(':')
-
-def add_lock(name):
-    """Add a lock to the list of held locks."""
-    locks = set(get_locks())
-    locks.add(name)
-    os.environ['REDO_LOCKS'] = ':'.join(list(locks))

redo/state.py

@@ -1,5 +1,5 @@
 import sys, os, errno, stat, fcntl, sqlite3
-import env
+import cycles, env
 from helpers import unlink, close_on_exec, join
 from logs import warn, debug2, debug3
 
@@ -24,10 +24,6 @@ STAMP_MISSING = '0'   # the stamp of a nonexistent file
 LOG_LOCK_MAGIC = 0x10000000  # fid offset for "log locks"
 
 
-class CyclicDependencyError(Exception):
-    pass
-
-
 def _connect(dbfile):
     _db = sqlite3.connect(dbfile, timeout=TIMEOUT)
     _db.execute("pragma synchronous = off")
@@ -466,9 +462,7 @@ class Lock(object):
 
     def check(self):
         assert not self.owned
-        if str(self.fid) in env.get_locks():
-            # Lock already held by parent: cyclic dependence
-            raise CyclicDependencyError()
+        cycles.check(self.fid)
 
     def trylock(self):
         self.check()