.\" Ouroboros man pages CC-BY 2017 - 2024 .\" Dimitri Staessens .\" Sander Vrijders .TH FLOW_ALLOC 3 2018-10-05 Ouroboros "Ouroboros Programmer's Manual" .SH NAME flow_accept, flow_alloc, flow_dealloc \- allocate and free resources to support Inter-Process Communication .SH SYNOPSIS .B #include \fBint flow_accept(qosspec_t * \fIqs\fB, const struct timespec * \fItimeo\fB); int flow_alloc(const char * \fIdst_name\fB, qosspec_t * \fIqs\fB, const struct timespec * \fItimeo\fB); int flow_join(const char * \fIdst_name\fB, qosspec_t * \fIqs\fB, const struct timespec * \fItimeo\fB); \fBint flow_dealloc(int \fIfd\fB);\fR Compile and link with \fI-louroboros-dev\fR. .SH DESCRIPTION These calls are used to allocate and free system and network resources to support Inter-Process Communication (IPC). Such a collection of allocated system and network resources is referred to as a flow. A flow has a certain Quality of Service (QoS) associated with it. The \fBflow_accept\fR() function blocks the calling thread waiting for an incoming request to allocate a flow. If \fBqosspec_t * \fIqs\fR is not NULL, the value of \fIqs\fR will be updated to reflect the actual QoS provided by the IPC facility for the accepted flow. Which flows this process will accept is configured through the IRMd. For an explanation on configuring which flows an application should accept, see \fBirm\fR(8). The \fBflow_alloc\fR() function requests to allocate system and/or network resources to support Inter-Process Communication between the calling application and one or more processes accepting flows for \fBchar * \fIdst_name\fR, which cannot be NULL. The \fBflow_alloc\fR() call can specify a certain minimum \fBqosspec_t * \fIqs\fR that has to be guaranteed by the IPC facility allocating the resources. This can be NULL if there is no QoS to be guaranteed (best effort service). If \fIqs\fR is not NULL, the value of \fIqs\fR will be updated to reflect the actual QoS provided by the IPC facility. The \fBflow_accept\fR() and \fBflow_alloc\fR() take a \fBconst struct timespec * \fItimeo\fR to specify a timeout. If \fItimeo\fR is NULL, the call will block indefinitely or until some error condition occurs. The \fBflow_join\fR() function allows applications to join a broadcast flow provided by a broadcast layer. The dst is the layer name. The \fBflow_dealloc\fR() function will release any resources associated with the flow. This call may block and keep reliable flows active until all packets are acknowledged. A \fBqosspec_t\fR specifies the QoS characteristics of a flow. The fields are: .TP \fBdelay\fR (ms) Maximum one-way delay. .TP \fBbandwidth\fR (bits/s) Minimum bandwidth. .TP \fBavailability\fR Class of 9s (e.g. 5 = 99.999%). .TP \fBloss\fR Tolerated packet loss; 0 selects reliable delivery. .TP \fBber\fR Tolerated bit error rate (errors per billion bits); 0 enables an end-to-end integrity check (corrupted packets are dropped). .TP \fBservice\fR Framing / reliability class: \fBSVC_RAW\fR (0) disables FRCT; \fBSVC_MESSAGE\fR (1) preserves SDU boundaries; \fBSVC_STREAM\fR (2) is a byte stream with no SDU boundaries. \fBSVC_STREAM\fR requires \fIloss\fR = 0; otherwise \fBflow_alloc\fR()/\fBflow_accept\fR() returns \fB-EINVAL\fR. .TP \fBmax_gap\fR (ms) Maximum tolerated inter-packet gap. Packets exceeding the gap budget are dropped under the real-time cubes. .TP \fBtimeout\fR (ms) Peer-liveness timeout; 0 disables. Only applies when FRCT is enabled (service > 0). .PP The library provides predefined cubes: .TP \fBqos_raw\fR No guarantees, no integrity check. .TP \fBqos_raw_safe\fR Best-effort with end-to-end integrity (ber = 0). .TP \fBqos_rt\fR / \fBqos_rt_safe\fR Real-time messages, optimised for latency over reliability; \fBqos_rt_safe\fR adds an end-to-end integrity check. .TP \fBqos_msg\fR Reliable, SDU-preserving delivery. .TP \fBqos_stream\fR Reliable byte stream; no SDU boundaries are preserved. .SH RETURN VALUE On success, \fBflow_accept\fR() and \fBflow_alloc\fR() calls return a non-negative integer, referred to as a flow descriptor. On failure, a negative value indicating the error will be returned. .SH ERRORS \fBflow_accept\fR(), \fBflow_alloc\fR() and \fBflow_dealloc\fR() can return the following errors: .B -EINVAL An invalid argument was passed. .B -EIRMD Failed to contact an IRMd instance. \fBflow_accept\fR() and \fBflow_alloc\fR() can also return .B -EBADF No more flow desciptors or flow_ids available. .B -ENOMEM Not enough system memory resources available to allocate the flow. .B -ETIMEDOUT Flow allocation timed out. .B -ECRYPT The requested encryption is not supported. .SH ATTRIBUTES For an explanation of the terms used in this section, see \fBattributes\fR(7). .TS box, tab(&); LB|LB|LB L|L|L. Interface & Attribute & Value _ \fBflow_accept\fR() & Thread safety & MT-Safe _ \fBflow_alloc\fR() & Thread safety & MT-Safe _ \fBflow_join\fR() & Thread safety & MT-Safe _ \fBflow_dealloc\fR() & Thread safety & MT-Safe .TE .SH NOTES The returned file descriptor is subject to a single-reader and single-writer discipline \(em at most one thread may call .BR flow_read () (or monitor the fd via .BR fevent ()) and at most one thread may call .BR flow_write () concurrently. See .BR flow_read (3), .BR flow_write (3), and .BR fevent (3) for details. .PP .BR flow_dealloc () must not be called concurrently with any thread that is inside .BR flow_read (), .BR flow_write (), .BR fevent (), or any other Ouroboros library call on the same fd; the result is undefined behaviour. Applications must serialise teardown with in-flight use, e.g. by signalling worker threads to drop the fd before calling .BR flow_dealloc (). .SH TERMINOLOGY Please see \fBouroboros-glossary\fR(7). .SH SEE ALSO .BR fccntl "(3), " fevent "(3), " flow_read "(3), " flow_write "(3), " \ fqueue "(3), " fset "(3), " ouroboros (8) .SH COLOPHON This page is part of the Ouroboros project, found at http://ouroboros.rocks These man pages are licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/