WSGI: 一个协议，描述通用服务器与python app之间的接口规范
wsgi app：遵守wsgi规范的python app
mod_wsgi： apache服务器的一个扩展模块, wsgi协议在apache服务器上的一个实现，有了它， 你就可以在apache上运行wsgi app
总的来说，WSGIScriptAlias 模式，python解释器被嵌入到apache进程当中，请求处理代码是在apache的 worker子进程中执行。WSGIDaemonProcess python解释器运行在单独的进程之中，和apache进程是隔离的。
mod_wsgi怎么完成python初始化？和apache关系怎样？一个简单的http请求进来之后， 处理流程大概是什么？下面将针对 WSGIScriptAlias 模式进行简要分析。
apache配置:
WSGIScriptAlias /hello /var/www/hello.wsgi
告诉apache hello.wsgi是一个mod_wsgi app，所有 /hello/ 下面的请求都转发给它。
wsgi代码:
jaime@westeros:~/source/mod-wsgi-3.3$ ls build-2.6 build-3.2 debian Makefile.in mod_wsgi.lo posix-ap2X.mk.in win32-ap22py31.mk build-2.7 configure LICENCE mod_wsgi.c mod_wsgi.slo README build-3.1 configure.ac Makefile mod_wsgi.la posix-ap1X.mk.in win32-ap22py26.mk
mod_wsgi.c有很多代码是关于apache 1.3的，和2.0代码有很多重名的函数，容易误导， 不便于阅读，可使用 unifdef 工具，将1.3相关的代码全部用空行替代，保留行号 的同时又清爽了许多:
jaime@westeros:~/source/mod-wsgi-3.3$ sudo apt-get install unifdef jaime@westeros:~/source/mod-wsgi-3.3$ unifdef -DAP_SERVER_MAJORVERSION_NUMBER=2 -b mod_wsgi.c > mod_wsgi-clean.c
apache模块的入口 mod_wsgi.c +15085
/* Dispatch list for API hooks */
module AP_MODULE_DECLARE_DATA wsgi_module = {
STANDARD20_MODULE_STUFF,
wsgi_create_dir_config, /* create per-dir config structures */
wsgi_merge_dir_config, /* merge per-dir config structures */
wsgi_create_server_config, /* create per-server config structures */
wsgi_merge_server_config, /* merge per-server config structures */
wsgi_commands, /* table of config file commands */
wsgi_register_hooks /* register hooks */
};
配置选项对应的函数 mod_wsgi.c +14982:
static const command_rec wsgi_commands[] =
{
AP_INIT_RAW_ARGS("WSGIScriptAlias", wsgi_add_script_alias,
NULL, RSRC_CONF, "Map location to target WSGI script file."),
...
#if defined(MOD_WSGI_WITH_DAEMONS)
AP_INIT_RAW_ARGS("WSGIDaemonProcess", wsgi_add_daemon_process,
NULL, RSRC_CONF, "Specify details of daemon processes to start."),
...
AP_INIT_TAKE1("WSGILazyInitialization", wsgi_set_lazy_initialization,
NULL, RSRC_CONF, "Enable/Disable lazy Python initialization."),
#endif
...
};
wsgi_add_script_alias大致做了一些初始化的工作，告诉apache dispatcher留意了， 看到类似XXX的url，要调用我们来处理。
有意思的是这个 wsgi_register_hooks mod_wsgi.c +14931+:
static void wsgi_register_hooks(apr_pool_t *p)
{
...
static const char * const p6[] = { "mod_python.c", NULL };
ap_hook_post_config(wsgi_hook_init, p6, NULL, APR_HOOK_MIDDLE);
ap_hook_child_init(wsgi_hook_child_init, p6, NULL, APR_HOOK_MIDDLE);
ap_hook_translate_name(wsgi_hook_intercept, p1, n1, APR_HOOK_MIDDLE);
ap_hook_handler(wsgi_hook_handler, NULL, NULL, APR_HOOK_MIDDLE);
...
}
从名字上看，wsgi_hook_init, wsgi_hook_child_init是做初始化工作的。 我们先看wsgi_hook_handler做了什么 mod_wsgi.c +8690:
static int wsgi_hook_handler(request_rec *r)
{
...
/*
* Only process requests for this module. First check for
* where target is the actual WSGI script. Then need to
* check for the case where handler name mapped to a handler
* script definition.
*/
// blablabla 一堆参数检查代码
...
/* Build the sub process environment. */
// wsgi协议相关环境变量在这里设置，每次请求都不一样
// 故此处是每次请求的必经之地
wsgi_build_environment(r);
...
// WSGIDaemonProcess 模式处理代码
/*
* Execute the target WSGI application script or proxy
* request to one of the daemon processes as appropriate.
*/
#if defined(MOD_WSGI_WITH_DAEMONS)
status = wsgi_execute_remote(r);
if (status != DECLINED)
return status;
#endif
...
return wsgi_execute_script(r);
}
wsgi_hook_handler 是每次请求的入口，最后调用wsgi_execute_script mod_wsgi.c +6404:
static int wsgi_execute_script(request_rec *r)
{
...
/* Grab request configuration. */
config = (WSGIRequestConfig *)ap_get_module_config(r->request_config,
&wsgi_module);
/*
* Acquire the desired python interpreter. Once this is done
* it is safe to start manipulating python objects.
*/
// 获得解释器，一个wsgi app可以运行在单独的python解释器里
// 在一个进程里，可以有多个解释器同时运行
// application_group 在 wsgi_application_group 函数中设置
// 与req请求的servername，port，scriptname有关，每次请求对应于哪个解释器由它来决定
interp = wsgi_acquire_interpreter(config->application_group);
if (!interp) {
ap_log_rerror(APLOG_MARK, WSGI_LOG_CRIT(0), r,
"mod_wsgi (pid=%d): Cannot acquire interpreter '%s'.",
getpid(), config->application_group);
return HTTP_INTERNAL_SERVER_ERROR;
}
/* Calculate the Python module name to be used for script. */
if (config->handler_script && *config->handler_script)
script = config->handler_script;
else
script = r->filename;
// 找到这个app的python模块名字
name = wsgi_module_name(r->pool, script);
...
modules = PyImport_GetModuleDict();
module = PyDict_GetItemString(modules, name);
Py_XINCREF(module);
if (module)
exists = 1;
/*
* If script reloading is enabled and the module for it has
* previously been loaded, see if it has been modified since
* the last time it was accessed. For a handler script will
* also see if it contains a custom function for determining
* if a reload should be performed.
*/
// Reload相关代码，检测app代码是否被修改
if (module && config->script_reloading) {
if (wsgi_reload_required(r->pool, r, script, module, r->filename)) {
...
#if defined(MOD_WSGI_WITH_DAEMONS)
if (*config->process_group) {
/*
* Need to restart the daemon process. We bail
* out on the request process here, sending back
* a special response header indicating that
* process is being restarted and that remote
* end should abandon connection and attempt to
* reconnect again. We also need to signal this
* process so it will actually shutdown. The
* process supervisor code will ensure that it
* is restarted.
*/
Py_BEGIN_ALLOW_THREADS
ap_log_rerror(APLOG_MARK, WSGI_LOG_INFO(0), r,
"mod_wsgi (pid=%d): Force restart of "
"process '%s'.", getpid(),
config->process_group);
Py_END_ALLOW_THREADS
...
wsgi_release_interpreter(interp);
r->status = HTTP_INTERNAL_SERVER_ERROR;
r->status_line = "0 Rejected";
wsgi_daemon_shutdown++;
// WSGIDaemonProcess 模式，杀掉当前daemon进程，重新加载
kill(getpid(), SIGINT);
return OK;
}
else {
...
PyDict_DelItemString(modules, name);
}
#else
/*
* Need to reload just the script module. Remove
* the module from the modules dictionary before
* reloading it again. If code is executing
* within the module at the time, the callers
* reference count on the module should ensure
* it isn't actually destroyed until it is
* finished.
*/
// WSGIScriptAlias 模式，删除旧的模块
PyDict_DelItemString(modules, name);
#endif
}
}
...
// 如果是第一次请求，则需要加载该模块
/* Load module if not already loaded. */
if (!module) {
module = wsgi_load_source(r->pool, r, name, exists, script,
config->process_group,
config->application_group);
}
...
// 激动人心的时刻到了，执行app代码！
status = HTTP_INTERNAL_SERVER_ERROR;
/* Determine if script exists and execute it. */
if (module) {
PyObject *module_dict = NULL;
PyObject *object = NULL;
module_dict = PyModule_GetDict(module);
object = PyDict_GetItemString(module_dict, config->callable_object);
if (object) {
AdapterObject *adapter = NULL;
adapter = newAdapterObject(r);
if (adapter) {
PyObject *method = NULL;
PyObject *args = NULL;
Py_INCREF(object);
status = Adapter_run(adapter, object); // 这里，这里
Py_DECREF(object);
...
}
else {
Py_BEGIN_ALLOW_THREADS
ap_log_rerror(APLOG_MARK, WSGI_LOG_ERR(0), r,
"mod_wsgi (pid=%d): Target WSGI script '%s' does "
"not contain WSGI application '%s'.",
getpid(), script, config->callable_object);
Py_END_ALLOW_THREADS
status = HTTP_NOT_FOUND;
}
}
// 错误处理
/* Log any details of exceptions if execution failed. */
if (PyErr_Occurred())
wsgi_log_python_error(r, NULL, r->filename);
/* Cleanup and release interpreter, */
Py_XDECREF(module);
wsgi_release_interpreter(interp);
return status;
}
Adapter_run +3823:
static int Adapter_run(AdapterObject *self, PyObject *object)
{
...
vars = Adapter_environ(self);
// 获取 start_response 函数
start = PyObject_GetAttrString((PyObject *)self, "start_response");
// 准备参数，还记得 def application(environ, start_response) 吗？
args = Py_BuildValue("(OO)", vars, start);
// 执行app代码
self->sequence = PyEval_CallObject(object, args);
if (self->sequence != NULL) {
if (!Adapter_process_file_wrapper(self)) {
int aborted = 0;
iterator = PyObject_GetIter(self->sequence);
if (iterator != NULL) {
PyObject *item = NULL;
// 遍历返回的iterator，输出每一行
while ((item = PyIter_Next(iterator))) {
...
if (length && !Adapter_output(self, msg, length, 0)) {
if (!PyErr_Occurred())
aborted = 1;
Py_DECREF(item);
break;
}
}
}
...
}
// 如果返回的seq有close方法则调用
if (PyObject_HasAttrString(self->sequence, "close")) {
PyObject *args = NULL;
PyObject *data = NULL;
close = PyObject_GetAttrString(self->sequence, "close");
args = Py_BuildValue("()");
data = PyEval_CallObject(close, args);
Py_DECREF(args);
Py_XDECREF(data);
Py_DECREF(close);
}
...
}
...
}
AdapterObject 是自定义的python类型，用来运行wsgi程序，含有start_response方法:
typedef struct {
PyObject_HEAD
int result;
request_rec \*r;
#if defined(MOD_WSGI_WITH_BUCKETS)
apr_bucket_brigade \*bb;
#endif
WSGIRequestConfig \*config;
InputObject \*input;
PyObject \*log;
int status;
const char \*status_line;
PyObject \*headers;
PyObject \*sequence;
int content_length_set;
apr_off_t content_length;
apr_off_t output_length;
} AdapterObject;
static PyTypeObject Adapter_Type;
...
static PyMethodDef Adapter_methods[] = {
{ "start_response", (PyCFunction)Adapter_start_response, METH_VARARGS, 0 },
{ "write", (PyCFunction)Adapter_write, METH_VARARGS, 0 },
{ "file_wrapper", (PyCFunction)Adapter_file_wrapper, METH_VARARGS, 0 },
{ NULL, NULL}
};
Adapter_xxx 系列函数，是wsgi协议的具体实现。我承认，前面说的在wsgi_build_environment中设置wsgi相关变量的说法有不对 的地方，大多数变量是在 Adapter_environ 中设置的:)
Adapter_start_response C实现的start_response
如何获得解释器?:
static InterpreterObject *wsgi_acquire_interpreter(const char *name)
{
PyThreadState *tstate = NULL;
PyInterpreterState *interp = NULL;
InterpreterObject *handle = NULL;
...
/*
* Check if already have interpreter instance and
* if not need to create one.
*/
handle = (InterpreterObject *)PyDict_GetItemString(wsgi_interpreters,
name);
if (!handle) {
// 如果没有查找到解释器，新解释器在这里被创建
handle = newInterpreterObject(name);
...
// 存储到 wsgi_interpreters
PyDict_SetItemString(wsgi_interpreters, name, (PyObject *)handle);
}
else
Py_INCREF(handle);
interp = handle->interp;
/*
* Create new thread state object. We should only be
* getting called where no current active thread
* state, so no need to remember the old one. When
* working with the main Python interpreter always
* use the simplified API for GIL locking so any
* extension modules which use that will still work.
*/
// thread 相关代码
...
return handle;
}
加载app代码在wsgi_load_source函数:
static PyObject *wsgi_load_source(apr_pool_t *pool, request_rec *r,
const char *name, int exists,
const char* filename,
const char *process_group,
const char *application_group)
{
...
fp = fopen(filename, "r");
n = PyParser_SimpleParseFile(fp, filename, Py_file_input);
...
co = (PyObject *)PyNode_Compile(n, filename);
PyNode_Free(n);
// 根据文件名字name，编译过的代码co，加载该模块
if (co)
m = PyImport_ExecCodeModuleEx((char *)name, co, (char *)filename);
Py_XDECREF(co);
if (m) {
...
// 设置模块修改时间
PyModule_AddObject(m, "__mtime__", object);
}
else {
Py_BEGIN_ALLOW_THREADS
if (r) {
ap_log_rerror(APLOG_MARK, WSGI_LOG_ERR(0), r,
"mod_wsgi (pid=%d): Target WSGI script '%s' cannot "
"be loaded as Python module.", getpid(), filename);
}
...
wsgi_log_python_error(r, NULL, filename);
}
return m;
}
以上即是WSGIScriptAlias模式下，一个请求收到之后，apache调用wsgi_hook_handler, mod_wsgi的大致处理流程。还有一个问题，python环境到底是在什么时候初始化的呢？ 让我们回头看。
wsgi_hook_init mod_wsgi.c +13031:
static int wsgi_hook_init(apr_pool_t *pconf, apr_pool_t *ptemp,
apr_pool_t *plog, server_rec *s)
{
...
/* Retain reference to base server. */
wsgi_server = s;
/* Retain record of parent process ID. */
wsgi_parent_pid = getpid();
/* Determine whether multiprocess and/or multithread. */
ap_mpm_query(AP_MPMQ_IS_THREADED, &wsgi_multithread);
wsgi_multithread = (wsgi_multithread != AP_MPMQ_NOT_SUPPORTED);
ap_mpm_query(AP_MPMQ_IS_FORKED, &wsgi_multiprocess);
if (wsgi_multiprocess != AP_MPMQ_NOT_SUPPORTED) {
ap_mpm_query(AP_MPMQ_MAX_DAEMONS, &wsgi_multiprocess);
wsgi_multiprocess = (wsgi_multiprocess != 1);
}
/* Retain reference to main server config. */
wsgi_server_config = ap_get_module_config(s->module_config, &wsgi_module);
/*
* Check that the version of Python found at
* runtime is what was used at compilation.
*/
wsgi_python_version();
/*
* Initialise Python if required to be done in
* the parent process. Note that it will not be
* initialised if mod_python loaded and it has
* already been done.
*/
if (wsgi_python_required == -1)
wsgi_python_required = 1;
// 在哪里初始化python，取决于 wsgi_python_after_fork 即 WSGILazyInitialization 选项
// 是在apache进程fork之前，还是之后？
if (!wsgi_python_after_fork)
wsgi_python_init(pconf);
/* Startup separate named daemon processes. */
// WSGIDaemonProcess 模式下启动daemon进程，要探索daemon模式的奥秘，这里即是入口
#if defined(MOD_WSGI_WITH_DAEMONS)
status = wsgi_start_daemons(pconf);
#endif
return status;
}
fork 之后的初始化函数:
static void wsgi_hook_child_init(apr_pool_t *p, server_rec *s)
{
...
// wsgi_python_required 取决于 WSGIRestrictEmbedded 选项
if (wsgi_python_required) {
/*
* Initialise Python if required to be done in
* the child process. Note that it will not be
* initialised if mod_python loaded and it has
* already been done.
*/
if (wsgi_python_after_fork)
wsgi_python_init(p);
/*
* Now perform additional initialisation steps
* always done in child process.
*/
wsgi_python_child_init(p);
}
}
这两个只是和apache相关的，由apache调用的hook初始化，真正的python初始化在 wsgi_python_init, wsgi_python_child_init 两步初始化:
static void wsgi_python_init(apr_pool_t *p)
{
static int initialized = 1;
/* Perform initialisation if required. */
if (!Py_IsInitialized() || !initialized) {
...
/* Initialise Python. */
ap_log_error(APLOG_MARK, WSGI_LOG_INFO(0), wsgi_server,
"mod_wsgi (pid=%d): Initializing Python.", getpid());
initialized = 1;
Py_Initialize(); // 神秘而又强大的 Py_Initialize
/* Initialise threading. */
PyEval_InitThreads();
#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 2
/*
* We now want to release the GIL. Before we do that
* though we remember what the current thread state is.
* We will use that later to restore the main thread
* state when we want to cleanup interpreters on
* shutdown.
*/
wsgi_main_tstate = PyThreadState_Get();
PyEval_ReleaseThread(wsgi_main_tstate);
#else
PyThreadState_Swap(NULL);
PyEval_ReleaseLock();
#endif
wsgi_python_initialized = 1;
/*
* Register cleanups to be performed on parent restart
* or shutdown. This will destroy Python itself.
*/
apr_pool_cleanup_register(p, NULL, wsgi_python_parent_cleanup,
apr_pool_cleanup_null);
}
}
static void wsgi_python_child_init(apr_pool_t *p)
{
// 第二步初始化所做的工作, 此时已经fork了
/*
* Trigger any special Python stuff required after a fork.
* Only do this though if we were responsible for the
* initialisation of the Python interpreter in the first
* place to avoid it being done multiple times. Also only
* do it if Python was initialised in parent process.
*/
/* Finalise any Python objects required by child process. */
/* Initialise Python interpreter instance table and lock. */
// 存放所有解释器的字典
wsgi_interpreters = PyDict_New();
/*
* Initialise the key for data related to a thread. At
* the moment we only record an integer thread ID to be
* used in lookup table to thread states associated with
* an interprter.
*/
/*
* Cache a reference to the first Python interpreter
* instance. This interpreter is special as some third party
* Python modules will only work when used from within this
* interpreter. This is generally when they use the Python
* simplified GIL API or otherwise don't use threading API
* properly. An empty string for name is used to identify
* the first Python interpreter instance.
*/
/* Loop through import scripts for this process and load them. */
// 处理wsgi_import_list
if (wsgi_import_list) {
...
}
}
ha, 终于快完了，现在，让我们打印一些有趣的输出，来看一看这些函数在什么时间， 哪个进程被调用。注意，下面的patch针对没有使用过 unifdef 的代码:
diff --git a/mod_wsgi.c b/mod_wsgi.c
index f0764b8..1781f7b 100644
--- a/mod_wsgi.c
+++ b/mod_wsgi.c
@@ -29,6 +29,8 @@
*
*/
+#define INFO(fmt, args...) ap_log_error(APLOG_MARK, WSGI_LOG_ERR(0), wsgi_server, "[pid %d] %s:%s:%d "fmt, getpid(),__FILE__, __PRETTY_FUNCTION__, __LINE__,args)
+
#define CORE_PRIVATE 1
#include "httpd.h"
@@ -5722,10 +5724,14 @@ static void wsgi_python_init(apr_pool_t *p)
static int initialized = 1;
#endif
+ INFO("%s", "enter");
+
/* Perform initialisation if required. */
if (!Py_IsInitialized() || !initialized) {
+ INFO("%s", "init python");
+
/* Enable Python 3.0 migration warnings. */
#if PY_MAJOR_VERSION == 2 && PY_MINOR_VERSION >= 6
@@ -5859,6 +5865,8 @@ static PyObject *wsgi_interpreters = NULL;
static InterpreterObject *wsgi_acquire_interpreter(const char *name)
{
+ INFO("search interpreter %s", name);
+
PyThreadState *tstate = NULL;
PyInterpreterState *interp = NULL;
InterpreterObject *handle = NULL;
@@ -5893,6 +5901,9 @@ static InterpreterObject *wsgi_acquire_interpreter(const char *name)
name);
if (!handle) {
+
+ INFO("create interpreter %s", name);
+
handle = newInterpreterObject(name);
if (!handle) {
@@ -5916,6 +5927,8 @@ static InterpreterObject *wsgi_acquire_interpreter(const char *name)
else
Py_INCREF(handle);
+ INFO("found interpreter %s", name);
+
interp = handle->interp;
/*
@@ -6339,6 +6352,8 @@ static int wsgi_execute_script(request_rec *r)
* it is safe to start manipulating python objects.
*/
+ INFO("%s", "enter");
+
interp = wsgi_acquire_interpreter(config->application_group);
if (!interp) {
@@ -6543,6 +6558,7 @@ static int wsgi_execute_script(request_rec *r)
PyObject *method = NULL;
PyObject *args = NULL;
+ INFO("%s", "app running");
Py_INCREF(object);
status = Adapter_run(adapter, object);
Py_DECREF(object);
@@ -6693,6 +6709,8 @@ static void wsgi_python_child_init(apr_pool_t *p)
int thread_id = 0;
int *thread_handle = NULL;
+ INFO("%s", "init python further");
+
/* Working with Python, so must acquire GIL. */
state = PyGILState_Ensure();
@@ -6778,6 +6796,9 @@ static void wsgi_python_child_init(apr_pool_t *p)
/* Loop through import scripts for this process and load them. */
if (wsgi_import_list) {
+
+ INFO("%s", "dealing with wsgi_import_list");
+
apr_array_header_t *scripts = NULL;
WSGIScriptFile *entries;
@@ -8115,6 +8136,7 @@ static void wsgi_log_script_error(request_rec *r, const char *e, const char *n)
static void wsgi_build_environment(request_rec *r)
{
+ INFO("%s", "enter");
WSGIRequestConfig *config = NULL;
const char *value = NULL;
@@ -8862,6 +8884,7 @@ static int wsgi_hook_handler(request_rec *r)
if (!r->handler)
return DECLINED;
+ INFO("handler %s, file %s", r->handler, r->filename);
/*
* Construct request configuration and cache it in the
* request object against this module so can access it later
@@ -9082,6 +9105,7 @@ static int wsgi_hook_handler(request_rec *r)
#if AP_SERVER_MAJORVERSION_NUMBER < 2
+
/*
* Apache 1.3 module initialisation functions.
*/
@@ -12909,6 +12933,9 @@ static int wsgi_hook_daemon_handler(conn_rec *c)
static int wsgi_hook_init(apr_pool_t *pconf, apr_pool_t *ptemp,
apr_pool_t *plog, server_rec *s)
{
+
+ INFO("%s", "enter");
+
void *data = NULL;
const char *userdata_key = "wsgi_init";
char package[128];
@@ -13028,6 +13055,8 @@ static void wsgi_hook_child_init(apr_pool_t *p, server_rec *s)
}
#endif
+ INFO("%s", "enter");
+
if (wsgi_python_required) {
/*
* Initialise Python if required to be done in
@@ -13500,6 +13529,7 @@ static authn_status wsgi_check_password(request_rec *r, const char *user,
* the last time it was accessed.
*/
+ /* FIXME: Reloading */
if (module && config->script_reloading) {
if (wsgi_reload_required(r->pool, r, script, module, NULL)) {
/*
@@ -14804,6 +14834,9 @@ static int wsgi_hook_logio(apr_pool_t *pconf, apr_pool_t *ptemp,
static void wsgi_register_hooks(apr_pool_t *p)
{
+
+ INFO("%s", "enter");
+
static const char * const p1[] = { "mod_alias.c", NULL };
static const char * const n1[]= { "mod_userdir.c",
"mod_vhost_alias.c", NULL };
日志输出，对应于上面给出的apache配置文件:
[Fri Sep 30 14:22:20 2011] [error] [pid 21372] mod_wsgi.c:wsgi_hook_init:12937 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21372] mod_wsgi.c:wsgi_register_hooks:14838 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21373] mod_wsgi.c:wsgi_hook_init:12937 enter [Fri Sep 30 14:22:20 2011] [notice] Apache/2.2.17 (Ubuntu) mod_wsgi/3.3 Python/2.7.1+ configured -- resuming normal operations [Fri Sep 30 14:22:20 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_child_init:13058 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21377] mod_wsgi.c:wsgi_python_init:5727 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21377] mod_wsgi.c:wsgi_python_init:5733 init python [Fri Sep 30 14:22:20 2011] [error] [pid 21378] mod_wsgi.c:wsgi_hook_child_init:13058 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21378] mod_wsgi.c:wsgi_python_init:5727 enter [Fri Sep 30 14:22:20 2011] [error] [pid 21378] mod_wsgi.c:wsgi_python_init:5733 init python [Fri Sep 30 14:22:20 2011] [error] [pid 21377] mod_wsgi.c:wsgi_python_child_init:6712 init python further [Fri Sep 30 14:22:20 2011] [error] [pid 21378] mod_wsgi.c:wsgi_python_child_init:6712 init python further jaime@westeros:/var/www$ ps aux | grep apache2 jaime 20827 0.0 0.0 3928 508 pts/2 S+ 14:17 0:00 tail -f /var/log/apache2/error.log root 21373 0.0 0.1 10224 3036 ? Ss 14:22 0:00 /usr/sbin/apache2 -k start www-data 21377 0.0 0.3 234368 6752 ? Sl 14:22 0:00 /usr/sbin/apache2 -k start www-data 21378 0.0 0.3 234392 6500 ? Sl 14:22 0:00 /usr/sbin/apache2 -k start jaime 23119 0.0 0.0 4156 856 pts/3 S+ 16:37 0:00 grep --color=auto apache2
启动apache之后，在主进程21372中，执行wsgi_hook_init, wsgi_register_hooks， 其中wsgi_hook_init 在另一个进程中21373中也被执行了。 创建了两个子进程21377, 21378。每个进程都按顺序执行wsgi_hook_child_init, wsgi_python_init, wsgi_python_child_init。 此时，apache已经启动完成，python也已经初始化，但是解释器还没有创建。
第一次请求，由进程21377负责处理，创建了解释器，也加载了hello.wsgi:
[Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler wsgi-script, file /var/www/hello.wsgi [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_build_environment:8139 enter [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6355 enter [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5868 search interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5905 create interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5930 found interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:29 2011] [info] [client 127.0.0.1] mod_wsgi (pid=21377, process='', application='127.0.1.1|/hello'): Loading WSGI script '/var/www/hello.wsgi'. [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6561 app running [Fri Sep 30 14:22:29 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler image/x-icon, file /var/www/favicon.ico [Fri Sep 30 14:22:29 2011] [error] [client 127.0.0.1] File does not exist: /var/www/favicon.ico
第二次请求，什么也不需要做，解释器使用原来的，代码也已经加载过了，cool:
[Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler wsgi-script, file /var/www/hello.wsgi [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_build_environment:8139 enter [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6355 enter [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5868 search interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5930 found interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6561 app running [Fri Sep 30 14:22:36 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler image/x-icon, file /var/www/favicon.ico [Fri Sep 30 14:22:36 2011] [error] [client 127.0.0.1] File does not exist: /var/www/favicon.ico
第三次请求，修改了hello.wsgi，所以需要重新加载代码, reloading:
[Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler wsgi-script, file /var/www/hello.wsgi [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_build_environment:8139 enter [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6355 enter [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5868 search interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_acquire_interpreter:5930 found interpreter 127.0.1.1|/hello [Fri Sep 30 14:22:47 2011] [info] [client 127.0.0.1] mod_wsgi (pid=21377, process='', application='127.0.1.1|/hello'): Reloading WSGI script '/var/www/hello.wsgi'. [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_execute_script:6561 app running [Fri Sep 30 14:22:47 2011] [error] [pid 21377] mod_wsgi.c:wsgi_hook_handler:8887 handler image/x-icon, file /var/www/favicon.ico [Fri Sep 30 14:22:47 2011] [error] [client 127.0.0.1] File does not exist: /var/www/favicon.ico
虽然前三次请求都由21372执行，但我们确实观测到了21378:
[Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_hook_handler:8887 handler wsgi-script, file /var/www/hello.wsgi [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_build_environment:8139 enter [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_execute_script:6355 enter [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_acquire_interpreter:5868 search interpreter 127.0.1.1|/hello [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_acquire_interpreter:5905 create interpreter 127.0.1.1|/hello [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_acquire_interpreter:5930 found interpreter 127.0.1.1|/hello [Fri Sep 30 14:41:37 2011] [info] [client 127.0.0.1] mod_wsgi (pid=21378, process='', application='127.0.1.1|/hello'): Loading WSGI script '/var/www/hello.wsgi'. [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_execute_script:6561 app running [Fri Sep 30 14:41:37 2011] [error] [pid 21378] mod_wsgi.c:wsgi_hook_handler:8887 handler image/x-icon, file /var/www/favicon.ico [Fri Sep 30 14:41:37 2011] [error] [client 127.0.0.1] File does not exist: /var/www/favicon.ico
Notes:
- Python c api代码和apache c代码混在一起，其实只不过是对不同lib的变量进行操作罢了， 实际上都是c代码。当把libpython，libapache链接到本进程时，它们有各自的变量在全局空间里, 保存着自己的状态，其他的代码就是对这些变量的操作。 这部分解释了为什么mod_python, mod_wsgi会冲突，因为他们都链接了同一个库libpython， 如果协调 不善，则极易出问题。 http://code.google.com/p/modwsgi/wiki/InstallationIssues#Incompatible_ModPython_Versions
wsgi_daemon_index 存放process_group到socket的一个映射， 由进程组的名字， 可以找到该组 进程正在监听的socket， 这个socket是与daemon通信的关键， 在fork之前创建， fork之后所有的子进程 都可访问， daemon需要关掉所有不是本进程组的socket fd。
wsgi_daemon_lists 所有已启动的daemon进程列表。
在apache启动的时候， 由wsgi_hook_init 调用start_daemons，创建所有的daemons， 此后daemon的数量就是固定的了。
pid7838 wsgi_hook_init调用返回之后， apache 又fork起了一个子进程 pid 7843， 非root权限， 调用wsgi_hook_child_init，此进程 负责处理分发所有的请求， 对每个请求调用wsgi_hook_handler， 在wsgi_execute_remote中和真正的daemon进程通过 socket进行交互， 该apache子进程可以被成为modwsgi的dispatcher。pid 7842是一个daemon进程。
不管是embedded模式， 还是daemon模式， 最后都会走到wsgi_execute_script函数。
请求headers， 标准的CGI变量， 是通过r->subprocess_env传递到daemon进程中的， 参见wsgi_build_environment, wsgi_send_request。 对象r，从dispatcher到daemon， 跨越了不同的进程， 已经不是原来的r了， 这点需要注意。
daemon进程如果发现需要reload代码， 则会发送一个0 Rejected 消息给dispatcher, 然后杀掉自己。apache捕获到daemon子进程死掉的信号， 重新启动一个daemon process， 仍然监听同一个socket。
daemon如果发现一切正常， 不需要reload（新的daemon总是如此）， 会发送0 Continue的消息给dispatcher， 告诉它可以go on了。
dispatcher如果收到0 Rejected信号， 会重新尝试连接，直到收到0 Continue或超出重试次数为止。实际上， 0 Continue可以被看作是一种同步机制。
[Sun Oct 30 13:00:17 2011] [error] [pid 7837] mod_wsgi.c:wsgi_hook_init:13658 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7837] mod_wsgi.c:wsgi_register_hooks:15564 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_hook_init:13658 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_python_init:5817 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_python_init:5823 init python [Sun Oct 30 13:00:17 2011] [info] mod_wsgi (pid=7838): Python home /usr/local/sae/python. [Sun Oct 30 13:00:17 2011] [info] mod_wsgi (pid=7838): Initializing Python. [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_start_daemons:11955 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_start_process:11540 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_start_process:11944 ok, we're father [Sun Oct 30 13:00:17 2011] [error] [pid 7838] mod_wsgi.c:wsgi_hook_init:13754 forking a new process to listen all connections, will call wsgi_hook_child_init [Sun Oct 30 13:00:17 2011] [warn] pid file /var/run/apache2.pid overwritten -- Unclean shutdown of previous Apache run? [Sun Oct 30 13:00:17 2011] [notice] Apache/2.2.17 (Ubuntu) mod_wsgi/3.3 Python/2.6.7 configured -- resuming normal operations [Sun Oct 30 13:00:17 2011] [info] Server built: Sep 1 2011 09:25:26 [Sun Oct 30 13:00:17 2011] [error] [pid 7843] mod_wsgi.c:wsgi_hook_child_init:13784 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7843] mod_wsgi.c:wsgi_python_child_init:6883 init python further [Sun Oct 30 13:00:17 2011] [info] mod_wsgi (pid=7843): Attach interpreter ''. [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_start_process:11558 ok in child, we're a new daemon process [Sun Oct 30 13:00:17 2011] [info] mod_wsgi (pid=7842): Starting process 'wic' with uid=1000, gid=1000 and threads=1. [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_python_child_init:6883 init python further [Sun Oct 30 13:00:17 2011] [info] mod_wsgi (pid=7842): Attach interpreter ''. [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_daemon_main:11276 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_daemon_main:11428 creating thread 0 [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_daemon_thread:11119 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_daemon_worker:10887 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_monitor_thread:11181 enter [Sun Oct 30 13:00:17 2011] [error] [pid 7842] mod_wsgi.c:wsgi_monitor_thread:11203 check worker status