Introducción
El soporte para el Control de Procesos en PHP implementa el estilo UNIX de
creación de procesos, ejecución de programas, gestión de señales y terminación
de procesos. El Control de Procesos no debería estar habilitado en un
entorno de servidor web, ya que podrían ocurrir resultados inesperados si cualquier
función del Control de Procesos es usada dentro de dichos entornos.
Esta documentación busca explicar el uso general de cada una de
las funciones del Control de Procesos. Para obtener información
detallada sobre el control de procesos de UNIX se recomienda consultar la
documentación del sistema incluyendo fork(2), waitpid(2) y signal(2)
o una referencia completa, como el libro "Advanced Programming in the
UNIX Environment" de W. Richard Stevens (Addison-Wesley).
PCNTL ahora usa pulsos (ticks) como mecanismo de retrollamada de manejadores de señal, que es
mucho más rápido que el mecanismo previo. Este cambio sigue la misma semántica
que usar "pulsos de usuario". Se usa la sentencia declare()
para especificar los lugares del programa donde se permiten que sucedan
las retrollamadas. Esto te permite minimizar la sobrecarga de manejar
eventos asincrónicos. En el pasado, compilar PHP con pcntl habilitado
siempre provocaba esta sobrecarga, sin importar si el script realmente empleaba
pcntl.
Nota: Esta extensión no
está disponible en plataformas Windows.
sean dot kelly at mediatile dot com ¶13 years ago
The following statement left me searching for answers for about a day before I finally clued in:"Process Control should not be enabled within a web server environment and unexpected results may happen if any Process Control functions are used within a web server environment."At least for PHP 5.3.8 which I am using, and who knows how far back, it's not a matter of "should not", it's "can not". Even though I have compiled in PCNTL with --enable-pcntl, it turns out that it only compiles in to the CLI version of PHP, not the Apache module. As a result, I spent many hours trying to track down why function_exists('pcntl_fork') was returning false even though it compiled correctly. It turns out it returns true just fine from the CLI, and only returns false for HTTP requests. The same is true of ALL of the pcntl_*() functions.
Rick Sustek ¶9 years ago
Actually it makes perfect sense why process control features are not supported for the Apache module. The Apache HTTP server is the chief process. It invokes the PHP module when steered to PHP by the resource requested (e.g. http://foo.php) It invokes the PHP module, typically on a new thread or a pooled thread. The PHP module then runs your script, but Apache server is still the owning process.In this execution model, the job of your PHP script is generally to go about its business as fast as possible and return. This allows the Apache daemon to do something else useful with the thread it let you borrow. Yes, some scripts take longer to do their duty than others, but blocking the thread for extended periods is usually frowned upon.If your script was allowed to mess with the signal handlers of the running process, it would be messing with the Apache daemon itself! That daemon has already installed signal handlers for its own use. It is just plain sense not to allow the process control operations in this context.
InvisibleSmiley ¶4 years ago
The disabling of pcntl functions not only affects Apache servers but any non-CLI setup, e.g. nginx with PHP-FPM.You can tell by issuing phpinfo() and looking at "disable_functions" in the Core section of the output.It's also worth noting that this behavior can be quite misleading when you call one of the pcntl functions in a namespaced context. For example you may get:"Call to undefined function some\custom\namespace\pcntl_signal()"when calling pcntl_signal from a method within a namespaced class. Your first instinct may be to add a leading backslash, but that won't solve the problem. You need to check whether the function exists at runtime, unless the code is only ever executed from the CLI.
