[PATCH 6/6] fetch2: Switch to shared locking for read accesses

Instead of always using an exclusive lock, use a shared lock for unpack
and the initial checks of download. This should mean that if we don't
need to make any writes to the download directory, we only ever need
the shared lock. As soon as any writes are possible, switch to the full
lock.

Also take advanatge of being able to pass None to the lock functions.

Signed-off-by: Richard Purdie <[email protected]>
---
 lib/bb/fetch2/__init__.py | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/lib/bb/fetch2/__init__.py b/lib/bb/fetch2/__init__.py
index 2676e0962b9..b6006fa38d7 100644
--- a/lib/bb/fetch2/__init__.py
+++ b/lib/bb/fetch2/__init__.py
@@ -1097,7 +1097,8 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
     # False means try another url
 
     try:
-        if ud.lockfile and ud.lockfile != origud.lockfile:
+        lf = None
+        if ud.lockfile != origud.lockfile:
             lf = bb.utils.lockfile(ud.lockfile)
 
         if check:
@@ -1174,7 +1175,7 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
             pass
         return False
     finally:
-        if ud.lockfile and ud.lockfile != origud.lockfile:
+        if ud.lockfile != origud.lockfile:
             bb.utils.unlockfile(lf)
 
 def try_mirrors(fetch, d, origud, mirrorvar, check = False):
@@ -1911,14 +1912,15 @@ class Fetch(object):
             done = False
 
             try:
-                if ud.lockfile:
-                    lf = bb.utils.lockfile(ud.lockfile)
+                lf = bb.utils.lockfile(ud.lockfile, shared=True)
 
                 self.d.setVar("BB_NO_NETWORK", network)
                 if m.verify_donestamp(ud, self.d) and not m.need_update(ud, self.d):
                     done = True
-                elif m.try_premirror(ud, self.d):
-                    done = m.try_mirrors(self, ud, self.d, 'PREMIRRORS')
+                if not done:
+                    bb.utils.lockfile_to_exclusive(lf)
+                    if m.try_premirror(ud, self.d):
+                        done = m.try_mirrors(self, ud, self.d, 'PREMIRRORS')
 
                 d = self.d
                 if premirroronly:
@@ -1980,8 +1982,7 @@ class Fetch(object):
                 raise
 
             finally:
-                if ud.lockfile:
-                    bb.utils.unlockfile(lf)
+                bb.utils.unlockfile(lf)
         if checksum_missing_messages:
             logger.error("Missing SRC_URI checksum, please add those to the recipe: \n%s", "\n".join(checksum_missing_messages))
             raise BBFetchException("There was some missing checksums in the recipe")
@@ -2031,8 +2032,7 @@ class Fetch(object):
                 ud = self.ud[u]
                 ud.setup_localpath(self.d)
 
-                if ud.lockfile:
-                    lf = bb.utils.lockfile(ud.lockfile)
+                lf = bb.utils.lockfile(ud.lockfile, shared=True)
 
                 unpack_tracer.start_url(u)
                 if update:
@@ -2042,8 +2042,7 @@ class Fetch(object):
                 unpack_tracer.finish_url(u)
 
             finally:
-                if ud.lockfile:
-                    bb.utils.unlockfile(lf)
+                bb.utils.unlockfile(lf)
 
         unpack_tracer.complete()
 
@@ -2068,16 +2067,14 @@ class Fetch(object):
                 if not ud.localfile and ud.localpath is None:
                     continue
 
-                if ud.lockfile:
-                    lf = bb.utils.lockfile(ud.lockfile)
+                lf = bb.utils.lockfile(ud.lockfile)
 
                 ud.method.clean(ud, self.d)
                 if ud.donestamp:
                     bb.utils.remove(ud.donestamp)
 
             finally:
-                if ud.lockfile:
-                    bb.utils.unlockfile(lf)
+                bb.utils.unlockfile(lf)
 
     def expanded_urldata(self, urls=None):
         """