To avoid closing the body fd prematurely, the fd value is moved from
the request struct to the app link. The body fd should not be closed
immediately after the request is sent to the application due to possible
request rescheduling.
If kqueue reported both the EVFILT_READ and the EVFILT_WRITE events
for the socket but only the former had the EV_EOF flag set, the flag
was silently ignored.
It allows proceeding to another action if a file isn't available.
An example:
{
"share": "/data/www/",
"fallback": {
"pass": "applications/php"
}
}
In the example above, an attempt is made first to serve a request with
a file from the "/data/www/" directory. If there's no such file, the
request is passed to the "php" application.
Fallback actions may be nested:
{
"share": "/data/www/",
"fallback": {
"share": "/data/cache/",
"fallback": {
"proxy": "http://127.0.0.1:9000"
}
}
}
For each request, the worker calls the php_execute_script function
from libphp that changes to the script directory before doing its
work and then restores the process directory before returning. The
chdir(2) calls it performs are unnecessary in Unit design. In simple
benchmarks, profiling shows that the chdir syscall code path (syscall,
FS walk, etc.) is where the CPU spends most of its time.
PHP SAPI semantics requires the script to be run from the script
directory. In Unit's PHP implementation, we have two use cases:
- script
- arbitrary path
The "script" configuration doesn't have much need for a working
directory change: it can be changed once at module initialization.
The module needs to chdir again only if the user's PHP script also
calls chdir to switch to another directory during execution.
If "script" is not used in Unit configuration, we must ensure the
script is run from its directory (thus calling chdir before exec),
but there's no need to restore the working directory later.
Our implementation disables mandatory chdir calls with the SAPI
option SAPI_OPTION_NO_CHDIR, instead calling chdir only when needed.
To detect the user's calls to chdir, a simple "unit" extension is
added that hooks the built-in chdir() PHP call.
Router built with debug may stop with assertion during stalled requests
re-schedule. This was caused by missing reference counting increment
before nxt_router_port_select() call.
