chore: better logging/error msg

per4m/giltracer.py

@@ -34,6 +34,8 @@ class GilTracer:
     def __enter__(self):
         pid = os.getpid()
         cmd = f"perf record -e 'sched:*' --call-graph dwarf -k CLOCK_MONOTONIC --pid {pid} -o {self.perf_output}"
+        if self.verbose >= 2:
+            print(f"Running: {cmd}")
         args = shlex.split(cmd)
         self.perf = subprocess.Popen(args, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
         start_time = time.time()
@@ -45,6 +47,7 @@ class GilTracer:
             # we need to wait till perf creates the file
             time.sleep(0.1)
         else:
+            self.finish()
             raise OSError(f'perf did not create {self.perf_output}')
         start_size = os.path.getsize(self.perf_output)
         for _ in range(RETRIES):
@@ -54,12 +57,13 @@ class GilTracer:
             # we need to wait till perf writes
             time.sleep(0.1)
         else:
+            self.finish()
             raise OSError(f'perf did not write to {self.perf_output}')
         # and give perf a bit more time
         time.sleep(0.05)
         return self
 
-    def __exit__(self, *args):
+    def finish(self):
         self.perf.terminate()
         outs, errs = self.perf.communicate(timeout=5)
         if self.verbose >= 1:
@@ -70,7 +74,9 @@ class GilTracer:
         if self.perf.returncode not in [0, -signal.SIGTERM.value]:
             print(signal.SIGTERM)
             raise OSError(f'perf record fails, got exit code {self.perf.returncode}')
-        # import pdb; pdb.set_trace()
+
+    def __exit__(self, *args):
+        self.finish()
         if self.verbose >= 1:
             print('Wait for perf to finish...')
         self.perf.wait()
@@ -79,7 +85,7 @@ class GilTracer:
         verbose = '-q ' + '-v ' * self.verbose
         cmd = f"perf script -i {self.perf_output} --no-inline | per4m perf2trace -o {self.trace_output} {verbose}"
         if os.system(cmd) != 0:
-            raise OSError('Failed to run perf or per4m perf2trace')
+            raise OSError(f'Failed to run perf or per4m perf2trace, command:\n$ {cmd}')
 
 
 def main(argv=sys.argv):