The Real-Time Priority Inheritance Library (librtpi) is intended to bridge the gap between the glibc pthread implementation and a functionally correct priority inheritance for pthread locking primitives, such as pthread_mutex and pthread_condvar.

Specifically, priority based wakeup is required for correct operation, in contrast to the more time-based ordered wakeup groups in the glibc pthread condvar implementation.

A C library with C++ bindings are provided.

This library provides an API that is as close as possible to the POSIX pthread specification. Any changes or restrictions to this API are the result of ensuring priority based wakeup ordering and proper behavior in the context of real-time and priority inheritance requirements.

Wherever possible, the glibc pthread primitives and functions are used, and where necessary are wrapped or rewritten. When the glibc implementation is incompatible, a new mechanism is provided, e.g. the pthread_condvar specifically.

To encourage programming to the API, internal types specific to the implementation are opaque types, or private class members in the case of the C++ bindings (using the "Has a" vs. "Is a" inheritance model).

$ autoreconf --install
$ ./configure
$ make
$ ./test

The Real-Time Priority Inheritance Library is licensed under the Lesser GNU Public License. The LGPL was chosen to make it possible to link with libc libraries, reuse code from libc, and still be as broadly usable as possible in industry.

Copyright © 2018 VMware, Inc. All Rights Reserved.

• rtpi.h
• pi_mutex.c
• pi_cond.c

• rtpi.h
• librtpi.a
• librtpi.so

Wrapper to pthread_mutex_t guranteed to be initialized using a mutexattr with the PTHREAD_PRIO_INHERIT protocal set.

New primitive modeled after the POSIX pthread_cond_t, with the following modifications.

1. All wakeup events will wake the N highest priority waiters.
2. Waiters will be woken in priority FIFO order.
3. The associated mutex must be held when the condition variable is signaled or broadcast.
4. The associated mutex must be passed as a parameter to the signal and broadcast calls. The mutex is used to requeue woken waiters and avoid the "thundering herd" effect.

The PI Mutex API represents a subset of the Pthread Mutex API, written specifically for priority inheritance aware condition variables. The calls wrap a pthread_mutex_t internally, but it is not exposed to the caller to examine, manipulate, or pass directly.

Wrapper to pthread_mutex_init and pthread_mutexattr_setprotocol, ensuring PTHREAD_PRIO_INHERIT is set, and allows for the specification of process private or process shared.

The following attributes are not supported:

• PTHREAD_MUTEX_RECURSIVE
• PTHREAD_MUTEX_ERRORCHECK