android: elf_symbolizer.py: Add WaitForIdle() method.

This method of ELFSymbolizer can be used to wait for the
completion of all async tasks, then allow additional ones
to be performed after that.

This is unlike the Join(), which waits for completion then
terminates all addr2line processes immediately, making any
future call to SymbolizeAsync() crash at runtime.

BUG=755225
R=pasko@chromium.org, lizeb@chromium.org, agrieve@chromium.org,jbudorick@chromium.org

Change-Id: Iea50c5e06bf495390dc1bc50a81151e069841175
Reviewed-on: https://chromium-review.googlesource.com/1046846Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: David Turner <digit@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556459}

build/android/pylib/symbols/elf_symbolizer.py

@@ -185,6 +185,11 @@ class ELFSymbolizer(object):
 
     a2l.EnqueueRequest(addr, callback_arg)
 
+  def WaitForIdle(self):
+    """Waits for all the outstanding requests to complete."""
+    for a2l in self._a2l_instances:
+      a2l.WaitForIdle()
+
   def Join(self):
     """Waits for all the outstanding requests to complete and terminates."""
     for a2l in self._a2l_instances:

build/android/pylib/symbols/elf_symbolizer_unittest.py

@@ -117,6 +117,31 @@ class ELFSymbolizerTest(unittest.TestCase):
 
     symbolizer.Join()
 
+  def testWaitForIdle(self):
+    symbolizer = elf_symbolizer.ELFSymbolizer(
+        elf_file_path='/path/doesnt/matter/mock_lib1.so',
+        addr2line_path=_MOCK_A2L_PATH,
+        callback=self._callback,
+        max_concurrent_jobs=1)
+
+    # Test symbols with valid name but incomplete path.
+    addr = _INCOMPLETE_MOCK_ADDR
+    exp_name = 'mock_sym_for_addr_%d' % addr
+    exp_source_path = None
+    exp_source_line = None
+    cb_arg = (addr, exp_name, exp_source_path, exp_source_line, False)
+    symbolizer.SymbolizeAsync(addr, cb_arg)
+    symbolizer.WaitForIdle()
+
+    # Test symbols with no name or sym info.
+    addr = _UNKNOWN_MOCK_ADDR
+    exp_name = None
+    exp_source_path = None
+    exp_source_line = None
+    cb_arg = (addr, exp_name, exp_source_path, exp_source_line, False)
+    symbolizer.SymbolizeAsync(addr, cb_arg)
+    symbolizer.Join()
+
   def _RunTest(self, max_concurrent_jobs, num_symbols):
     symbolizer = elf_symbolizer.ELFSymbolizer(
         elf_file_path='/path/doesnt/matter/mock_lib1.so',