The Design and Implementation of the Synchronous Language CÉU

Abstract

C éU is a synchronous language targeting soft real-time systems. It is inspired by Esterel and has a simple semantics with fine-grain control over program execution. C éU uses an event-triggered notion of time that enables compile-time checks to detect conflicting concurrent statements, resulting in deterministic and concurrency-safe programs. We present the particularities of our design in comparison to Esterel, such as stack-based internal events, concurrency checks, safe integration with C, and first-class timers. We also present two implementation back ends: one aiming for resource efficiency and interoperability with C, and another as a virtual machine that allows remote reprogramming.

A Gals Approach for Pogramming Distributed Interactive Multimedia Applications

“…Distributed Interactive Multimedia Applications: Using Mars in Real-World Examples reacts to each occurrence of the event TOGGLE_VIDEO_STATE and pauses or resumes the scene depending on its current state (lines [15][16][17][18][19][20][21][22]. The second reacts to Céu-Media key input events (lines [23][24][25][26][27][28][29][30]. If the key is "space", it emits the event SPACE, or if the key is "escape", it emits the event TOGGLE_TOGETHERNESS.…”

“…In practice, this model assumes that computing reactions is much faster than the minimum time interval between external events, which is a feasible assumption in real-time embedded systems [21]. Esterel [22], Lustre [23], StateChart [24], Céu [25] are some examples of synchronous languages.…”

“…Céu [25] is a reactive synchronous language originally developed as a safe alternative for programming soft real-time embedded systems. Céu programs advance in a sequence of discrete reactions to external events received from their environments.…”

“…The par/or composition may end either when the second trail wakes from this await (i.e., the user has chosen a content to watch) or when the main video ends (i.e., first trail ends). If the user has interacted on his/her personal device, the chosen content will be presented, otherwise the default content is selected (lines [20][21][22][23][24][25][26][27].…”

“…The program then creates a parallel composition with 5 trails (lines 17-51). The fist requests a new slide to be presented whenever Alice presses the "space" key (lines [18][19][20][21][22][23][24][25]. The second waits for event REQUEST_CONTROL and, if there is no student controlling the video (i.e., the variable control is 0) it broadcasts to all students that one of them is now controlling it (i.e., it emits the event REPLY_CONTROL passing a student identifier)-lines 27-33.…”