1173 debug mode (#1176)

* implement PSUTIL_DEBUG from C module

* update doc

* add psutil_debug() utility function

* update doc

* enable PSUTIL_DEBUG for tests

* update appveyor.yml

* change psutil_debug() signature so that it can accept variable num of args

* provide DEBUG info in psutil_raise_for_pid()

* properly print debug message

* do not print too much

1 files changed, 9 insertions, 4 deletions

diff --git a/psutil/_psutil_posix.c b/psutil/_psutil_posix.c
index ea0fba53..76cf2db0 100644
--- a/psutil/_psutil_posix.c
+++ b/psutil/_psutil_posix.c
@@ -112,16 +112,21 @@ psutil_pid_exists(long pid) {
  * This will always set a Python exception and return NULL.
  */
 int
-psutil_raise_for_pid(long pid, char *msg) {
+psutil_raise_for_pid(long pid, char *syscall_name) {
     // Set exception to AccessDenied if pid exists else NoSuchProcess.
     if (errno != 0) {
+        // Unlikely we get here.
         PyErr_SetFromErrno(PyExc_OSError);
         return 0;
     }
-    if (psutil_pid_exists(pid) == 0)
+    else if (psutil_pid_exists(pid) == 0) {
+        psutil_debug("%s syscall failed and PID %i no longer exists; "
+                     "assume NoSuchProcess", syscall_name, pid);
         NoSuchProcess();
-    else
-        PyErr_SetString(PyExc_RuntimeError, msg);
+    }
+    else {
+        PyErr_Format(PyExc_RuntimeError, "%s syscall failed", syscall_name);
+    }
     return 0;
 }