Adding skeleton row locking code for demo

core/views.py

@@ -1 +1,81 @@
-# Create your views here.
+from regluit.core.models import Campaign
+from django.http import HttpResponse
+import traceback
+from django.db import transaction
+import time
+
+def test_read(request):
+    
+    try:
+        
+        row_id = 1
+        
+        print "Attempting to read row"
+        
+        # A read the waits for the exclusive lock for the row
+        campaign = Campaign.objects.raw("SELECT * FROM core_campaign WHERE id=%d FOR UPDATE" % row_id)[0]
+        
+        print "Successfully read row data %d" % campaign.target
+        
+    except:
+        traceback.print_exc()
+        
+    return HttpResponse("Success")
+
+def test_write(request):
+    
+    try:
+        
+        row_id = 1
+        campaign = Campaign.objects.get(id=row_id)
+        
+        print "Attempting to write row via ordinary ORM"
+        
+        #
+        # Modify the data.  This will block if any shared lock (Either FOR UPDATE or LOCK IN SHARED MODE is held
+        #
+        campaign.target = campaign.target + 10
+        campaign.save()
+        
+        print "Successfully write new row data %d" % campaign.target
+        
+    except:
+        traceback.print_exc()
+        
+    return HttpResponse("Success")
+
+@transaction.commit_on_success
+def test_lock(request):
+
+    try:
+        row_id = 1
+
+        print "Attempting to acquire row lock"
+
+        campaign = Campaign.objects.raw("SELECT * FROM core_campaign WHERE id=%d FOR UPDATE" % row_id)[0]
+
+        print "Row lock acquired, modifying data"
+
+        # Modify the data
+        campaign.target = campaign.target + 10
+        campaign.save()
+
+        #
+        # test by sleeping here for 10 seconds.  
+        #
+        # The FOR UPDATE request will lock the row exclusively.  All write/delete operations require a compatible lock
+        # and will block until this transaction is complete.  Some reads will block, but some will not.  If we want to
+        # block the read until this transaction is complete, the read should also acquire an exlusive OR a shared lock.
+        #
+        # As soon as the function completes, the transaction will be committed and the lock released.
+        # You can modify the commit_on_success decorator to get different transaction behaviors
+        #
+        print "Thread sleeping for 10 seconds"
+        time.sleep(10)
+        print "Thread sleep complete"
+
+    except:
+        traceback.print_exc()
+
+    return HttpResponse("Success")
+