This fixes file descriptor leakage in router. Shared memory file used to
send data from router to application. These files are shared among all
processes of same application and router keeps the opened file descriptor since
06017e6e3a5f commit.
The application process needs to request the shared memory segment from the
router instead of the latter pushing the segment before sending a request to
the application. This is required to simplify the communication between the
router and the application and to prepare the router for using the application
shared port and then the queue.
There is no restrictions on configration size and using segmented shared memory
only doubles memory usage because to parse configration on router side,
it needs to be 'plain' e. g. located in single continous memory buffer.
The process abstraction has changed to:
setup(task, process)
start(task, process_data)
prefork(task, process, mp)
The prefork() occurs in the main process right before fork.
The file src/nxt_main_process.c is completely free of process
specific logic.
The creation of a process now supports a PROCESS_CREATED state. The
The setup() function of each process can set its state to either
created or ready. If created, a MSG_PROCESS_CREATED is sent to main
process, where external setup can be done (required for rootfs under
container).
The core processes (discovery, controller and router) doesn't need
external setup, then they all proceeds to their start() function
straight away.
In the case of applications, the load of the module happens at the
process setup() time and The module's init() function has changed
to be the start() of the process.
The module API has changed to:
setup(task, process, conf)
start(task, data)
As a direct benefit of the PROCESS_CREATED message, the clone(2) of
processes using pid namespaces now doesn't need to create a pipe
to make the child block until parent setup uid/gid mappings nor it
needs to receive the child pid.
After 41331471eee7 completion handlers should complete next buffer in chain.
Otherwise buffer memory may leak.
Thanks to Peter Tkatchenko for reporing the issue and testing fixes.
- OOSM (out of shared memory). Sent by application process to router
when application reaches the limit of allocated shared memory and
needs more.
- SHM_ACK. Sent by router to application when the application's shared
memory is released and the OOSM flag is enabled for the segment.
This implements blocking mode (the library waits for SHM_ACK in case of
out of shared memory condition and retries allocating the required memory
amount) and non-blocking mode (the library notifies the application that
it's out of shared memory and returns control to the application module
that sets up the output queue and puts SHM_ACK in the main message loop).
Changeset #699 fixes shared memory allocation: continous buffer with
requested size should be allocated or function failed. For body longer
than 10 Mb, this allocation will definitely fails.
For body buffer it is not required to send it in a single continous buffer,
so, need to request minimum reasonable amount of shared memory and try to
extend it, if possible or allocate next buffer.
Previously, one shared memory chunk was allocated under mutex and other
chunks (if required) were allocated using atomic operations. So such
allocation is not guaranteed and the result buffer can be less than
requested.
This commit moves multiple chunks allocation under mutex and guarantees
the result buffer is large enough.
"All problems in computer science can be
solved by another level of indirection"
Butler Lampson
Completion handlers for application response buffers executed after
sending the data to client. Application worker can be stopped right
after send response buffers to router. Worker stop causes removal
of all data structures for the worker.
To prevent shared memory segment unmap, need to count the number of
buffers which uses it. So instead of direct reference to shared
memory, need to reference to intermediate 'handler' structure with
use counter and pointer to shared memory.
Two different router threads may send different requests to single
application worker. In this case shared memory fds from worker
to router will be send over 2 different router ports. These fds
will be received and processed by different threads in any order.
This patch made possible to add incoming shared memory segments in
arbitrary order. Additionally, array and memory pool are no longer
used to store segments because of pool's single threaded nature.
Custom array-like structure nxt_port_mmaps_t introduced.
This allows to use shared memory to communicate with main process.
This patch changes shared memory segment format and breaks compatibility
with older modules.
To allow use port from different threads, the first step is to avoid using
port's memory pool for temporary allocations required to send data through
the port. Including but not limited by:
- buffers for data;
- send message structures;
- new mmap fd notifications;
It is still safe to use port memory pool for incoming buffers allocations
because recieve operation bound to single thread.
Do not reuse shared memory segment with different port until this segment
successfully received and indexed on other side. However, segment can be used
to transfer data via the port it was sent at any time.
NXT_PORT_MSG_LAST - mark message as last;
NXT_PORT_MSG_CLOSE_FD - close fd right after send;
Type constants altered to include last flag for single buffer messages.
Last sign is critical for coming port RPC layer. Handlers unregistered on last
message. Create sync buffer is not convenient, extra parameter is better.
There is a case in router where we use port in router connection thread.
Buffers are allocated within connection memory pool which can be used only in
this router thread. sendmsg() can be postponed into main router thread and
completion handler will compare current engine and post itself to correct
engine.
nxt_port_mmap_t stored in arrays and it is unsafe to store
pointer to array element.
Shared memory structures and macros moved to separate header
file to be used by GO package.
