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.
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.
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User Contributed Notes 3 notes
sean dot kelly at mediatile dot com ¶
12 years ago
Rick Sustek ¶
8 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 ¶
3 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.
