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The socket is required for intercontextual communication in multithreaded apps.
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The PORT_ACK message is the router's response to the application's NEW_PORT
message. After receiving PORT_ACK, the application is safe to process requests
using this port.
This message avoids a racing condition when the application starts processing a
request from the shared queue and sends REQ_HEADERS_ACK. The REQ_HEADERS_ACK
message contains the application port ID as reply_port, which the router uses
to send request data. When the application creates a new port, it
immediately sends it to the main router thread. Because the request is
processed outside the main thread, a racing condition can occur between the
receipt of the new port in the main thread and the receipt of REQ_HEADERS_ACK
in the worker router thread where the same port is specified as reply_port.
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Until the mmap is received by the router, only the creator thread may use this
mmap, so the "mmap not found" state in the router is avoided.
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Data in the queue and the socket are transmitted independently; special
READ_QUEUE and READ_SOCKET message types are used for synchronization.
The warning was accidentally committed with changeset 1d84b9e4b459.
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Large-bodied requests are added to the request hash to be found when the body
arrives. However, changeset 1d84b9e4b459 introduced a bug: the 'in_hash' flag,
used to remove the request from the hash at request release, was cleared after
the first successful request lookup. As a result, the entry was never removed.
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This change aids heap usage analysis in applications.
The alloc and free functions are also required for lvlhash due to the upcoming
threading support, because using main nxt_memalign() and nxt_free() isn't safe
in a multithreaded app environment. The reason is that these functions may use
thread-local structures which aren't initialized properly in applications.
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Some of the pointers were not adjusted after frame's memory re-allocation.
Fortunately, this function was not used and the bug has no effect.
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Two consecutive fd and fd2 fields replaced with array.
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The default libunit behavior relies on blocking the recv() call for port file
descriptors, which an application may override if needed. For external
applications, port file descriptors were toggled to blocking mode before the
exec() call. If the exec() call failed, descriptor remained blocked, so the
process hanged while trying to read from it.
This patch moves file descriptor mode switch inside libunit.
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The goal is to minimize the number of syscalls needed to deliver a message.
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Generic process-to-process shared memory exchange is no more required. Here,
it is transformed into a router-to-application pattern. The outgoing shared
memory segments collection is now the property of the application structure.
The applications connect to the router only, and the process only needs to group
the ports.
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This is the port shared between all application processes which use it to pass
requests for processing. Using it significantly simplifies the request
processing code in the router. The drawback is 2 more file descriptors per each
configured application and more complex libunit message wait/read code.
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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.
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The application process needs to request the port from the router instead of the
latter pushing the port 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 to use the application shared port and then the queue.
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The goal is to minimize the number of (pid, id) to port hash lookups which
require a library mutex lock. The response port is found once per request,
while the read port is initialized at startup.
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- Changed the port management callbacks to notifications, which e. g. avoids
the need to call the libunit function
- Added context and library instance reference counts for a safer resource
release
- Added the router main port initialization
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This makes log format used in libunit consistent with the daemon, where milliseconds are printed only in the
debug log level.
Currently a compile time switch is used, since there's no support for runtime changing of a log level for now.
But in the future this should be a runtime condition, similar to nxt_log_time_handler().
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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.
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An earlier attempt (ad6265786871) to resolve this condition on the
router's side added a new issue: the app could get a request before
acquiring a port.
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Missing error log messages added.
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Main process exiting before app process init may have caused hanging.
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This is required for proper log file rotation action.
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This closes #386 on GitHub.
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Ruby and Java modules now use this function instead of own
implementations.
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This issue was introduced in 2c7f79bf0a1f.
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Uninitialized ctx_impl field may cause crash in application process.
To reproduce the issue, need to trigger shared memory buffer send error on
application side. In our case, send error caused by router process crash.
This issue was introduced in 2c7f79bf0a1f.
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Found by Coverity (CID 353386).
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- 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).
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The function unchains the buffer from the buffer's linked list.
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Current shared memory buffer implementation uses fixed-size memory blocks,
allocating at least 16384 bytes. When application sends data in a large
number of small chunks, it makes sense to buffer them or use plain
memory buffers to improve performance and reduce memory footprint.
This patch introduces minimum size limit (1024 bytes) for shared
memory buffers.
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Name and value in each header are 0-terminated, so additional 2 bytes
should be allocated for them. There were several attempts to add these
2 bytes to headers in language modules, but some modules weren't updated.
Also, adding these 2 bytes is specific to the implementation which may be
changed later, so extending this mechanics to modules may cause errors.
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Found by Coverity (CID 349456).
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Each request references the router process structure that owns all memory
maps. The process structure has a reference counter; each request increases
the counter to lock the structure in memory until request processing ends.
Incoming and outgoing buffers reference memory maps that the process owns,
so the process structure should be released only when all buffers are
released to avoid invalid memory access and a crash.
This describes the libunit library mechanism used for application processes.
The background of this issue is as follows:
The issue was found on buildbot when the router crashed during Java
websocket tests. The Java application receives a notification from the
master process; when the notification is processed, libunit deletes the
process structure from its process hash and decrements the use counter;
however, active websocket connections maintain their use counts on the
process structure. After that, when the master process is stopping the
application, libunit releases active websocket connections. At this point,
it's important to release the connections' memory buffers before the
corresponding process structure and all shared memory segments are released.
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One alert per failed allocation is enough.
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By design, Unit context is created for the thread which reads messages from
the router. However, Go request handlers are called in a separate goroutine
that may be executed in a different thread. To avoid a racing condition,
access to lists of free structures in the context should be serialized. This
patch should fix random crashes in Go applications under high load.
This is related to #253 and #309 issues on GitHub.
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