add research for usage for subprocess

+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+import sys, shlex, time, subprocess
+
+cmd = "./python.subprocess 0 800"
+args = shlex.split(str(cmd))
+print "cmd: %s, args: %s"%(cmd, args)
+
+def use_communicate(args, fout, ferr):
+    process = subprocess.Popen(args, stdout=fout, stderr=ferr)
+    (stdout_str, stderr_str) = process.communicate()
+    return (stdout_str, stderr_str)
+
+def use_poll(args, fout, ferr, timeout):
+    (stdout_str, stderr_str) = (None, None)
+    process = subprocess.Popen(args, stdout=fout, stderr=ferr)
+    starttime = time.time()
+    while True:
+        process.poll()
+        if process.returncode is not None:
+            (stdout_str, stderr_str) = process.communicate()
+            break
+        if timeout > 0 and time.time() - starttime >= timeout:
+            print "timeout, kill process. timeout=%s"%(timeout)
+            process.kill()
+            break
+        time.sleep(1)
+    process.wait()
+    return (stdout_str, stderr_str)
+def use_communicate_timeout(args, fout, ferr, timeout):
+    (stdout_str, stderr_str) = (None, None)
+    process = subprocess.Popen(args, stdout=fout, stderr=ferr)
+    starttime = time.time()
+    while True:
+
+fnull = open("/dev/null", "rw")
+fout = subprocess.PIPE#fnull.fileno()
+ferr = subprocess.PIPE#fnull#fnull.fileno()
+print "fout=%s, ferr=%s"%(fout, ferr)
+#(stdout_str, stderr_str) = use_communicate(args, fout, ferr)
+#(stdout_str, stderr_str) = use_poll(args, fout, ferr, 10)
+(stdout_str, stderr_str) = use_communicate_timeout(args, fout, ferr, 10)
+
+def print_result(stdout_str, stderr_str):
+    if stdout_str is None:
+        stdout_str = ""
+    if stderr_str is None:
+        stderr_str = ""
+    print "terminated, size of stdout=%s, stderr=%s"%(len(stdout_str), len(stderr_str))
+    while True:
+        time.sleep(1)
+
+print_result(stdout_str, stderr_str)

+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+/**
+# always to print to stdout and stderr.
+g++ python.subprocess.cpp -o python.subprocess
+*/
+int main(int argc, char** argv) {
+    if (argc <= 2) {
+        printf("Usage: <%s> <interval_ms> <max_loop>\n"
+            "   %s 50 100000\n", argv[0], argv[0]);
+        exit(-1);
+        return -1;
+    }
+    
+    int interval_ms = ::atoi(argv[1]);
+    int max_loop = ::atoi(argv[2]);
+    printf("always to print to stdout and stderr.\n");
+    printf("interval: %d ms\n", interval_ms);
+    printf("max_loop: %d\n", max_loop);
+    
+    for (int i = 0; i < max_loop; i++) {
+        fprintf(stdout, "always to print to stdout and stderr. interval=%dms, max=%d, current=%d\n", interval_ms, max_loop, i);
+        fprintf(stderr, "always to print to stdout and stderr. interval=%dms, max=%d, current=%d\n", interval_ms, max_loop, i);
+        if (interval_ms > 0) {
+            usleep(interval_ms * 1000);
+        }
+    }
+    
+    return 0;
+}