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2008-07-14 Joshua Tauberer <jit@occams.info>
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	* src/mod_mono.c: Always acquire a lock at the start of processing
	a request. The active requests counter function now assumes the
	lock is already aquired. Also added a accepting_requests flag
	to the dashboard so that xsp configurations can be paused. Now
	when restarting mod-mono-server from the control panel, the
	configuration is set to not accepting requests (503s returned)
	until after the restart. This fixed a problem that when requests
	came in during a restart, mod-mono-server would never successfully
	come back but it would keep getting forked. The flag can also
	be turned on and off through the control panel.

svn path=/trunk/mod_mono/; revision=107874
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Joshua Tauberer committed Jul 14, 2008
1 parent 637c6c3 commit 7cff8fb
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13 changes: 13 additions & 0 deletions ChangeLog
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@@ -1,3 +1,16 @@
2008-07-14 Joshua Tauberer <jit@occams.info>

* src/mod_mono.c: Always acquire a lock at the start of processing
a request. The active requests counter function now assumes the
lock is already aquired. Also added a accepting_requests flag
to the dashboard so that xsp configurations can be paused. Now
when restarting mod-mono-server from the control panel, the
configuration is set to not accepting requests (503s returned)
until after the restart. This fixed a problem that when requests
came in during a restart, mod-mono-server would never successfully
come back but it would keep getting forked. The flag can also
be turned on and off through the control panel.

2008-07-14 Marek Habersack <mhabersack@novell.com>

* src/mod_mono.c (write_string_to_buffer, send_initial_data): use
Expand Down
159 changes: 117 additions & 42 deletions src/mod_mono.c
View file
Expand Up @@ -65,6 +65,7 @@ typedef struct {
char restart_issued;
int active_requests;
int waiting_requests;
int accepting_requests;
} dashboard_data;

#define INITIAL_DATA_MAX_ALLOCA_SIZE 8192
Expand Down Expand Up @@ -466,6 +467,7 @@ ensure_dashboard_initialized (module_cfg *config, xsp_data *xsp, apr_pool_t *p)
xsp->dashboard->restart_issued = 0;
xsp->dashboard->active_requests = 0;
xsp->dashboard->waiting_requests = 0;
xsp->dashboard->accepting_requests = 1;
}
}
}
Expand Down Expand Up @@ -1996,6 +1998,13 @@ static int
increment_active_requests (xsp_data *conf)
{
#ifndef APACHE13
/* This function tries to increment the counters that limit
* the number of simultaenous requests being processed. It
* assumes that the mutex is held when the function is called
* and returns with the mutex still held, although it may
* unlock and lock the mutex itself.
*/

apr_status_t rv;

int max_active_requests = atoi(conf->max_active_requests);
Expand All @@ -2004,21 +2013,20 @@ increment_active_requests (xsp_data *conf)
/* Limit the number of concurrent requests. If no
* limiting is in effect (or can't be done because
* there is no dashboard), return the OK status.
* Same test as in the decrement function. */
if (max_active_requests == 0 || !conf->dashboard_mutex || !conf->dashboard)
* Same test as in the decrement function and the
* control panel. */
if (!conf->dashboard_mutex || !conf->dashboard)
return 1;

rv = apr_global_mutex_lock (conf->dashboard_mutex);
/* Drop the request on failure to lock the dashboard because
* we don't want to decrement the counter later since we couldn't
* increment it here. */
if (rv != APR_SUCCESS)
return 0;

// From here on, rv holds onto whether we still have
// the lock acquired, just in case some error ocurrs
// acquiring it during the loop.
if (conf->dashboard->active_requests >= max_active_requests) {
rv = APR_SUCCESS;

/* If any limiting is in effect, and if there are the maximum
* allowed concurrent requests, then we have to hold the request
* for a bit of time. */
if (max_active_requests > 0 && conf->dashboard->active_requests >= max_active_requests) {
/* We need to wait until the active requests
* go below the maximum. */

Expand All @@ -2028,7 +2036,6 @@ increment_active_requests (xsp_data *conf)
* is max_active_req+max_waiting_req.
*/
if (conf->dashboard->waiting_requests >= max_waiting_requests) {
apr_global_mutex_unlock (conf->dashboard_mutex);
ap_log_error (APLOG_MARK, APLOG_ERR, STATUS_AND_SERVER,
"Maximum number of concurrent mod_mono requests to %s reached (%d active, %d waiting). Request dropped.",
conf->dashboard_lock_file, max_active_requests, max_waiting_requests);
Expand Down Expand Up @@ -2063,7 +2070,6 @@ increment_active_requests (xsp_data *conf)
// many requests are going, stop processing the
// request.
if (rv == APR_SUCCESS && conf->dashboard->active_requests >= max_active_requests) {
apr_global_mutex_unlock (conf->dashboard_mutex);
ap_log_error (APLOG_MARK, APLOG_ERR, STATUS_AND_SERVER,
"Maximum number (%d) of concurrent mod_mono requests to %s reached. Droping request.",
max_active_requests, conf->dashboard_lock_file);
Expand All @@ -2078,7 +2084,6 @@ increment_active_requests (xsp_data *conf)
return 0;

conf->dashboard->active_requests++;
apr_global_mutex_unlock (conf->dashboard_mutex);

return 1;
#else
Expand All @@ -2092,11 +2097,9 @@ decrement_active_requests (xsp_data *conf)
#ifndef APACHE13
apr_status_t rv;

int max_active_requests = atoi(conf->max_active_requests);

/* Check if limiting is in effect. Same test as in the
* increment function. */
if (max_active_requests == 0 || !conf->dashboard_mutex || !conf->dashboard)
* increment function and the control panel. */
if (!conf->dashboard_mutex || !conf->dashboard)
return;

rv = apr_global_mutex_lock (conf->dashboard_mutex);
Expand Down Expand Up @@ -2194,12 +2197,23 @@ mono_execute_request (request_rec *r, char auto_app)
} else
conf->dashboard_mutex_initialized_in_child = 1;
}

if (conf->dashboard_mutex && conf->dashboard) {
if (apr_global_mutex_lock (conf->dashboard_mutex) == APR_SUCCESS) {
int ok = conf->dashboard->accepting_requests;
if (ok)
ok = increment_active_requests (conf);

apr_global_mutex_unlock (conf->dashboard_mutex);

if (!ok)
return HTTP_SERVICE_UNAVAILABLE;
}
}
#endif

rv = -1; /* avoid a warning about uninitialized value */
if (!increment_active_requests (conf))
return HTTP_SERVICE_UNAVAILABLE;


while (connect_attempts--) {
rv = setup_socket (&sock, conf, r->pool);
DEBUG_PRINT (2, "After setup_socket");
Expand Down Expand Up @@ -2603,6 +2617,31 @@ terminate_xsp (void *data)
return terminate_xsp2(data, NULL, 0, 0);
}

static void
set_accepting_requests (void *data, char *alias, int accepting_requests)
{
server_rec *server;
module_cfg *config;
xsp_data *xsp;
int i;

server = (server_rec *) data;
config = ap_get_module_config (server->module_config, &mono_module);

for (i = 0; i < config->nservers; i++) {
xsp = &config->servers [i];

/* If alias isn't null, skip XSPs that don't have that alias. */
if (alias != NULL && strcmp(xsp->alias, alias))
continue;

#ifndef APACHE13
if (xsp->dashboard)
xsp->dashboard->accepting_requests = accepting_requests;
#endif
}
}

static int
mono_control_panel_handler (request_rec *r)
{
Expand Down Expand Up @@ -2630,43 +2669,63 @@ mono_control_panel_handler (request_rec *r)
uri = &r->parsed_uri;
if (!uri->query || !strcmp (uri->query, "")) {
/* No query string -> Emit links for configuration commands. */
request_send_response_string (r, "<ul style=\"text-align: center;\">\n");
request_send_response_string (r, "<ul>\n");
request_send_response_string (r, "<li><div>All Backends</div>\n<ul>\n");
request_send_response_string (r, "<li><a href=\"?restart=ALL\">Restart all mod-mono-server processes</a></li>\n");
request_send_response_string (r, "<li><a href=\"?pause=ALL\">Stop Accepting Requests</a></li>\n");
request_send_response_string (r, "<li><a href=\"?resume=ALL\">Resume Accepting Requests</a></li>\n");
request_send_response_string (r, "</ul></li>\n");

for (i = 0; i < config->nservers; i++) {
xsp = &config->servers [i];
if (xsp->run_xsp && !strcasecmp (xsp->run_xsp, "false"))
continue;

buffer = apr_psprintf (r->pool, "<li>%s: <a href=\"?restart=%s\">"
"Restart Server</a>", xsp->alias, xsp->alias);
buffer = apr_psprintf (r->pool, "<li><div>%s</div><ul>\n", xsp->alias);
request_send_response_string(r, buffer);

buffer = apr_psprintf (r->pool, "<li><a href=\"?restart=%s\">Restart Server</a></li>\n", xsp->alias);
request_send_response_string(r, buffer);

#ifndef APACHE13
ensure_dashboard_initialized (config, xsp, pconf);
if (xsp->dashboard_mutex) {
rv = apr_global_mutex_lock (xsp->dashboard_mutex);
if (rv == APR_SUCCESS) {
if (xsp->restart_mode == AUTORESTART_MODE_REQUESTS) {
buffer = apr_psprintf (r->pool, " [%d requests served; limit: %d]",
xsp->dashboard->handled_requests, xsp->restart_requests);
request_send_response_string(r, buffer);
} else if (xsp->restart_mode == AUTORESTART_MODE_TIME) {
buffer = apr_psprintf (r->pool, " [%ds time running; limit: %ds]",
(int)(time(NULL) - xsp->dashboard->start_time), (int)xsp->restart_time);
request_send_response_string(r, buffer);
}

rv = apr_global_mutex_unlock (xsp->dashboard_mutex);
if (rv != APR_SUCCESS)
ap_log_error (APLOG_MARK, APLOG_ALERT, STATCODE_AND_SERVER (rv),
"Failed to release %s lock after mono-ctrl output, the process may deadlock!",
xsp->dashboard_lock_file);
if (xsp->dashboard_mutex && xsp->dashboard
&& apr_global_mutex_lock (xsp->dashboard_mutex) == APR_SUCCESS) {

if (xsp->dashboard->accepting_requests)
buffer = apr_psprintf (r->pool, "<li><a href=\"?pause=%s\">Stop Accepting Requests</a></li>\n", xsp->alias);
else
buffer = apr_psprintf (r->pool, "<li><a href=\"?resume=%s\">Resume Accepting Requests</a></li>\n", xsp->alias);
request_send_response_string(r, buffer);

if (xsp->restart_mode == AUTORESTART_MODE_REQUESTS) {
buffer = apr_psprintf (r->pool, "<li>%d requests served; limit: %d</li>\n",
xsp->dashboard->handled_requests, xsp->restart_requests);
request_send_response_string(r, buffer);
} else if (xsp->restart_mode == AUTORESTART_MODE_TIME) {
buffer = apr_psprintf (r->pool, "<li>%ds time running; limit: %ds</li>\n",
(int)(time(NULL) - xsp->dashboard->start_time), (int)xsp->restart_time);
request_send_response_string(r, buffer);
}

buffer = apr_psprintf (r->pool, "<li>%d requests currently being processed; limit: %s</li>\n",
xsp->dashboard->active_requests, xsp->max_active_requests);
request_send_response_string(r, buffer);

buffer = apr_psprintf (r->pool, "<li>%d requests currently waiting to be processed; limit: %s</li>\n",
xsp->dashboard->waiting_requests, xsp->max_waiting_requests);
request_send_response_string(r, buffer);


rv = apr_global_mutex_unlock (xsp->dashboard_mutex);
if (rv != APR_SUCCESS)
ap_log_error (APLOG_MARK, APLOG_ALERT, STATCODE_AND_SERVER (rv),
"Failed to release %s lock after mono-ctrl output, the process may deadlock!",
xsp->dashboard_lock_file);
}
#endif

request_send_response_string(r, "</li>\n");
request_send_response_string(r, "</ul></li>\n");
}

request_send_response_string (r, "</ul>\n");
Expand All @@ -2676,9 +2735,25 @@ mono_control_panel_handler (request_rec *r)
char *alias = uri->query + 8; /* +8 == .Substring(8) */
if (!strcmp (alias, "ALL"))
alias = NULL;
set_accepting_requests (r->server, alias, 0);
terminate_xsp2 (r->server, alias, 1, 0);
start_xsp (config, 1, alias);
set_accepting_requests (r->server, alias, 1);
request_send_response_string (r, "<div style=\"text-align: center;\">mod-mono-server processes restarted.</div><br>\n");
} else if (uri->query && !strncmp (uri->query, "pause=", 6)) {
/* Stop accepting requests for this server */
char *alias = uri->query + 6; /* +6 == .Substring(6) */
if (!strcmp (alias, "ALL"))
alias = NULL;
set_accepting_requests (r->server, alias, 0);
request_send_response_string (r, "<div style=\"text-align: center;\">no longer accepting requests</div><br>\n");
} else if (uri->query && !strncmp (uri->query, "resume=", 7)) {
/* Resume accepting requests for this server */
char *alias = uri->query + 7; /* +7 == .Substring(7) */
if (!strcmp (alias, "ALL"))
alias = NULL;
set_accepting_requests (r->server, alias, 1);
request_send_response_string (r, "<div style=\"text-align: center;\">resumed accepting requests</div><br>\n");
} else {
/* Invalid command. */
request_send_response_string (r, "<div style=\"text-align: center;\">Invalid query string command.</div>\n");
Expand Down

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