[PATCH 1/1] fetch2: Do not fail to create symbolic links if they already exist

[Peter Kjellerstedt <peter.kjellerstedt@axis.com>]

When the fetcher retrieves file:// URLs, there is no lock file being
used. This means that in case two separate tasks (typically from two
concurrent invocations of bitbake) want to download the same file://
URL at the same time, there is a very small chance that they also end
up wanting to create a symbolic link to the file at the same time.
This would previously lead to one of the tasks failing as the other
task would have created the link.

Signed-off-by: Peter Kjellerstedt <pkj@axis.com>
---
 bitbake/lib/bb/fetch2/__init__.py | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/bitbake/lib/bb/fetch2/__init__.py b/bitbake/lib/bb/fetch2/__init__.py
index ea72025c22..136fc29c16 100644
--- a/bitbake/lib/bb/fetch2/__init__.py
+++ b/bitbake/lib/bb/fetch2/__init__.py
@@ -983,7 +983,14 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
                 open(ud.donestamp, 'w').close()
             dest = os.path.join(dldir, os.path.basename(ud.localpath))
             if not os.path.exists(dest):
-                os.symlink(ud.localpath, dest)
+                # In case this is executing without any file locks held (as is
+                # the case for file:// URLs), two tasks may end up here at the
+                # same time, in which case we do not want the second task to
+                # fail when the link has already been created by the first task.
+                try:
+                    os.symlink(ud.localpath, dest)
+                except FileExistsError:
+                    pass
             if not verify_donestamp(origud, ld) or origud.method.need_update(origud, ld):
                 origud.method.download(origud, ld)
                 if hasattr(origud.method,"build_mirror_data"):
@@ -995,7 +1002,11 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
                 # Broken symbolic link
                 os.unlink(origud.localpath)
 
-            os.symlink(ud.localpath, origud.localpath)
+            # As per above, in case two tasks end up here simultaneously.
+            try:
+                os.symlink(ud.localpath, origud.localpath)
+            except FileExistsError:
+                pass
         update_stamp(origud, ld)
         return ud.localpath
 
-- 
2.12.0