#include <ApplicationPool.h>
Spawning Ruby on Rails application instances is a very expensive operation. Despite best efforts to make the operation less expensive (see SpawnManager), it remains expensive compared to the cost of processing an HTTP request/response. So, in order to solve this, some sort of caching/pooling mechanism will be required. ApplicationPool provides this.
Normally, one would use SpawnManager to spawn a new RoR application instance, then use Application::connect() to create a new session with that application instance, and then use the returned Session object to send the request and to read the HTTP response. ApplicationPool replaces the first step with a call to Application::get(). For example:
ApplicationPool pool = some_function_which_creates_an_application_pool(); // Connect to the application and get the newly opened session. Application::SessionPtr session(pool->get("/home/webapps/foo")); // Send the request headers and request body data. session->sendHeaders(...); session->sendBodyBlock(...); // Done sending data, so we close the writer channel. session->closeWriter(); // Now read the HTTP response. string responseData = readAllDataFromSocket(session->getReader()); // Done reading data, so we close the reader channel. session->closeReader(); // This session has now finished, so we close the session by resetting // the smart pointer to NULL (thereby destroying the Session object). session.reset(); // We can connect to an Application multiple times. Just make sure // the previous session is closed. session = app->connect("/home/webapps/bar")
Internally, ApplicationPool::get() will keep spawned applications instances in memory, and reuse them if possible. It will try to keep spawning to a minimum. Furthermore, if an application instance hasn't been used for a while, it will be automatically shutdown in order to save memory. Restart requests are honored: if an application has the file 'restart.txt' in its 'tmp' folder, then get() will shutdown existing instances of that application and spawn a new instance (this is useful when a new version of an application has been deployed). And finally, one can set a hard limit on the maximum number of applications instances that may be spawned (see ApplicationPool::setMax()).
Note that ApplicationPool is just an interface (i.e. a pure virtual class). For concrete classes, see StandardApplicationPool and ApplicationPoolServer. The exact pooling algorithm depends on the implementation class.
Public Member Functions | |
| virtual Application::SessionPtr | get (const string &appRoot, bool lowerPrivilege=true, const string &lowestUser="nobody")=0 |
Open a new session with the application specified by appRoot. | |
| virtual void | clear ()=0 |
| Clear all application instances that are currently in the pool. | |
| virtual void | setMax (unsigned int max)=0 |
| Set a hard limit on the number of application instances that this ApplicationPool may spawn. | |
| virtual unsigned int | getActive () const =0 |
| Get the number of active applications in the pool. | |
| virtual unsigned int | getCount () const =0 |
| Get the number of active applications in the pool. | |
| virtual pid_t | getSpawnServerPid () const =0 |
| Get the process ID of the spawn server that is used. | |
| virtual Application::SessionPtr Passenger::ApplicationPool::get | ( | const string & | appRoot, | |
| bool | lowerPrivilege = true, |
|||
| const string & | lowestUser = "nobody" | |||
| ) | [pure virtual] |
Open a new session with the application specified by appRoot.
See the class description for ApplicationPool, as well as Application::connect(), on how to use the returned session object.
Internally, this method may either spawn a new application instance, or use an existing one.
If lowerPrivilege is true, then any newly spawned application instances will have lower privileges. See SpawnManager::SpawnManager()'s description of lowerPrivilege and lowestUser for details.
| appRoot | The application root of a RoR application, i.e. the folder that contains 'app/', 'public/', 'config/', etc. This must be a valid directory, but does not have to be an absolute path. | |
| lowerPrivilege | Whether to lower the application's privileges. | |
| lowestUser | The user to fallback to if lowering privilege fails. |
| SpawnException | An attempt was made to spawn a new application instance, but that attempt failed. | |
| IOException | Something else went wrong. |
appRoot does not have to be absolute, it should be. If one calls get("/home/foo") and get("/home/../home/foo"), then ApplicationPool will think they're 2 different applications, and thus will spawn 2 application instances. Implemented in Passenger::StandardApplicationPool.
| virtual void Passenger::ApplicationPool::clear | ( | ) | [pure virtual] |
Clear all application instances that are currently in the pool.
This method is used by unit tests to verify that the implementation is correct, and thus should not be called directly.
Implemented in Passenger::StandardApplicationPool.
| virtual void Passenger::ApplicationPool::setMax | ( | unsigned int | max | ) | [pure virtual] |
Set a hard limit on the number of application instances that this ApplicationPool may spawn.
The exact behavior depends on the used algorithm, and is not specified by these API docs.
It is allowed to set a limit lower than the current number of spawned applications.
Implemented in Passenger::StandardApplicationPool.
| virtual unsigned int Passenger::ApplicationPool::getActive | ( | ) | const [pure virtual] |
Get the number of active applications in the pool.
This method exposes an implementation detail of the underlying pooling algorithm. It is used by unit tests to verify that the implementation is correct, and thus should not be called directly.
Implemented in Passenger::StandardApplicationPool.
| virtual unsigned int Passenger::ApplicationPool::getCount | ( | ) | const [pure virtual] |
Get the number of active applications in the pool.
This method exposes an implementation detail of the underlying pooling algorithm. It is used by unit tests to verify that the implementation is correct, and thus should not be called directly.
Implemented in Passenger::StandardApplicationPool.
| virtual pid_t Passenger::ApplicationPool::getSpawnServerPid | ( | ) | const [pure virtual] |
Get the process ID of the spawn server that is used.
This method exposes an implementation detail. It is used by unit tests to verify that the implementation is correct, and thus should not be used directly.
Implemented in Passenger::StandardApplicationPool.
1.5.3