Introdução

O suporte ao controle de processos em PHP implementa o estilo Unix de criação de processos, execução de programas, manipulação de sinais e encerramento de processos. O Controle de Processo não deve ser ativado em um ambiente de servidor web e resultados inesperados podem ocorrer se alguma função de Controle de Processo for usada em um ambiente de servidor web.

Esta documentação tem como objetivo explicar o uso geral de cada uma das funções de Controle de Processo. Para obter informações detalhadas sobre o controle de processos Unix, você é encorajado a consultar a documentação do seu sistema, incluindo fork(2), waitpid(2) e signal(2) ou uma referência abrangente, como Programação Avançada no Ambiente UNIX por W. Richard Stevens (Addison-Wesley).

PCNTL agora usa ticks como mecanismo de retorno de chamada de identificador de sinal, que é muito mais rápido que o mecanismo anterior. Esta mudança segue a mesma semântica do uso de "user ticks". Você usa a instrução declare() para especificar os locais em seu programa onde os retornos de chamada podem ocorrer. Isso permite minimizar a sobrecarga do tratamento de eventos assíncronos. No passado, compilar PHP com pcntl habilitado sempre incorreria nessa sobrecarga, independentemente de seu script usar pcntl ou não.

Nota: Esta extensão não está disponível em plataformas Windows.

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User Contributed Notes 3 notes

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sean dot kelly at mediatile dot com ¶

12 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.

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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.

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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.

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