[PATCH 2/3] cache/siggen: Add unihash cache copy function

[Richard Purdie <richard.purdie@linuxfoundation.org>]

We see rare failures in eSDK generation with zero sized unihash cache files. This is
almost certainly due to races in the cache file being updated. Add a copy function
where the cache file can be copied with the lock held to avoid this.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---
 lib/bb/cache.py  | 9 +++++++++
 lib/bb/siggen.py | 6 ++++++
 2 files changed, 15 insertions(+)

diff --git a/lib/bb/cache.py b/lib/bb/cache.py
index 92e9a3ced7..988c596c39 100644
--- a/lib/bb/cache.py
+++ b/lib/bb/cache.py
@@ -24,6 +24,7 @@ from collections.abc import Mapping
 import bb.utils
 from bb import PrefixLoggerAdapter
 import re
+import shutil
 
 logger = logging.getLogger("BitBake.Cache")
 
@@ -998,3 +999,11 @@ class SimpleCache(object):
             p.dump([data, self.cacheversion])
 
         bb.utils.unlockfile(glf)
+
+    def copyfile(self, target):
+        if not self.cachefile:
+            return
+
+        glf = bb.utils.lockfile(self.cachefile + ".lock")
+        shutil.copy(self.cachefile, target)
+        bb.utils.unlockfile(glf)
diff --git a/lib/bb/siggen.py b/lib/bb/siggen.py
index 08eca7860e..3f3d6df54d 100644
--- a/lib/bb/siggen.py
+++ b/lib/bb/siggen.py
@@ -120,6 +120,9 @@ class SignatureGenerator(object):
     def save_unitaskhashes(self):
         return
 
+    def copy_unitaskhashes(self, targetdir):
+        return
+
     def set_setscene_tasks(self, setscene_tasks):
         return
 
@@ -358,6 +361,9 @@ class SignatureGeneratorBasic(SignatureGenerator):
     def save_unitaskhashes(self):
         self.unihash_cache.save(self.unitaskhashes)
 
+    def copy_unitaskhashes(self, targetdir):
+        self.unihash_cache.copyfile(targetdir)
+
     def dump_sigtask(self, fn, task, stampbase, runtime):
 
         tid = fn + ":" + task
-- 
2.34.1