Make process_startup idempotent, to fix #340.

3 files changed, 30 insertions, 7 deletions

diff --git a/.hgignore b/.hgignore
index 41058479..c13de37d 100644
--- a/.hgignore
+++ b/.hgignore
@@ -23,8 +23,7 @@ dist
 htmlcov
 MANIFEST
 setuptools-*.egg
-.tox
-.tox_kits
+.tox*
 .noseids
 
 # Stuff in the test directory.
diff --git a/CHANGES.txt b/CHANGES.txt
index c0166bb8..d51d34c3 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -14,7 +14,12 @@ Latest
 - A new warning is possible, if a desired file isn't measured because it was
   imported before coverage was started (`issue 353`_).
 
+- The `coverage.process_startup` function now will start coverage measurement
+  only once, no matter how many times it is called.  This fixes problems due
+  to unusual virtualenv configurations (`issue 340`_).
+
 .. _issue 117: https://bitbucket.org/ned/coveragepy/issue/117/enable-coverage-measurement-of-code-run-by
+.. _issue 340: https://bitbucket.org/ned/coveragepy/issue/340/keyerror-subpy
 .. _issue 353: https://bitbucket.org/ned/coveragepy/issue/353/40a3-introduces-an-unexpected-third-case
 
 
diff --git a/coverage/control.py b/coverage/control.py
index f422d7c0..81653d31 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -1062,11 +1062,30 @@ def process_startup():
 
     """
     cps = os.environ.get("COVERAGE_PROCESS_START")
-    if cps:
-        cov = Coverage(config_file=cps, auto_data=True)
-        cov.start()
-        cov._warn_no_data = False
-        cov._warn_unimported_source = False
+    if not cps:
+        # No request for coverage, nothing to do.
+        return
+
+    # This function can be called more than once in a process. This happens
+    # because some virtualenv configurations make the same directory visible
+    # twice in sys.path.  This means that the .pth file will be found twice,
+    # and executed twice, executing this function twice.  We set a global
+    # flag (an attribute on this function) to indicate that coverage has
+    # already been started, so we can avoid doing it twice.
+    #
+    # https://bitbucket.org/ned/coveragepy/issue/340/keyerror-subpy has more
+    # details.
+
+    if hasattr(process_startup, "done"):
+        # We've annotated this function before, so we must have already
+        # started coverage in this process.  Nothing to do.
+        return
+
+    process_startup.done = True
+    cov = Coverage(config_file=cps, auto_data=True)
+    cov.start()
+    cov._warn_no_data = False
+    cov._warn_unimported_source = False
 
 
 # A hack for debugging testing in sub-processes.