test: do not use PIPE

as instructed in the python docs, you should not use PIPE here. This can
lead to deadlocks, with massive testsuite output. Which was the case for efl.
For now the output of the tests is redirected into the a temp file, the
content from there can then be used to fill the TestRun structure.

This fixes test running problems in efl.

mesonbuild/mtest.py

@@ -23,6 +23,7 @@ from mesonbuild.dependencies import ExternalProgram
 from mesonbuild.mesonlib import substring_is_in_list, MesonException
 from mesonbuild import mlog
 
+import tempfile
 import time, datetime, multiprocessing, json
 import concurrent.futures as conc
 import platform
@@ -289,8 +290,8 @@ class SingleTestRunner:
         stdout = None
         stderr = None
         if not self.options.verbose:
-            stdout = subprocess.PIPE
-            stderr = subprocess.PIPE if self.options and self.options.split else subprocess.STDOUT
+            stdout = tempfile.TemporaryFile("wb+")
+            stderr = tempfile.TemporaryFile("wb+") if self.options and self.options.split else stdout
 
         # Let gdb handle ^C instead of us
         if self.options.gdb:
@@ -324,7 +325,7 @@ class SingleTestRunner:
         else:
             timeout = self.test.timeout
         try:
-            (stdo, stde) = p.communicate(timeout=timeout)
+            p.communicate(timeout=timeout)
         except subprocess.TimeoutExpired:
             if self.options.verbose:
                 print('%s time out (After %d seconds)' % (self.test.name, timeout))
@@ -337,6 +338,8 @@ class SingleTestRunner:
                 # Let us accept ^C again
                 signal.signal(signal.SIGINT, previous_sigint_handler)
 
+        additional_error = None
+
         if kill_test or timed_out:
             # Python does not provide multiplatform support for
             # killing a process and all its children so we need
@@ -353,25 +356,31 @@ class SingleTestRunner:
                     # already died) so carry on.
                     pass
             try:
-                (stdo, stde) = p.communicate(timeout=1)
+                p.communicate(timeout=1)
             except subprocess.TimeoutExpired:
                 # An earlier kill attempt has not worked for whatever reason.
                 # Try to kill it one last time with a direct call.
                 # If the process has spawned children, they will remain around.
                 p.kill()
                 try:
-                    (stdo, stde) = p.communicate(timeout=1)
+                    p.communicate(timeout=1)
                 except subprocess.TimeoutExpired:
-                    stdo = b'Test process could not be killed.'
-                    stde = b''
+                    additional_error = b'Test process could not be killed.'
             except ValueError:
-                stdo = b'Could not read output. Maybe the process has redirected its stdout/stderr?'
-                stde = b''
+                additional_error = b'Could not read output. Maybe the process has redirected its stdout/stderr?'
         endtime = time.time()
         duration = endtime - starttime
-        stdo = decode(stdo)
-        if stde:
-            stde = decode(stde)
+        if additional_error is None:
+            stdout.seek(0)
+            stdo = decode(stdout.read())
+            if stderr != stdout:
+                stderr.seek(0)
+                stde = decode(stderr.read())
+            else:
+                stde = ""
+        else:
+            stdo = ""
+            stde = additional_error
         if timed_out:
             res = TestResult.TIMEOUT
         elif p.returncode == GNU_SKIP_RETURNCODE: