Protothreads

Protothreads are extremely lightweight stackless threads designed for severely memory constrained systems, such as small embedded systems or wireless sensor network nodes. Protothreads provide linear code execution for event-driven systems implemented in C. Protothreads can be used with or without an underlying operating system to provide blocking event-handlers. Protothreads provide sequential flow of control without complex state machines or full multi-threading.

#include "pt.h" struct pt pt; struct timer timer; PT_THREAD(example(struct pt *pt)) { PT_BEGIN(pt); while(1) { if(initiate_io()) { timer_start(&timer); PT_WAIT_UNTIL(pt, io_completed() || timer_expired(&timer)); read_data(); } } PT_END(pt); } Example protothreads code. Example protothreads code.

While protothreads originally were created for memory-constrained embedded systems, it has found many uses as a general purpose library too. Examples include multimedia streaming server software, grid computing research software, and MPEG decoding software for Internet TVs.

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Main features:

Very small RAM overhead - only two bytes per protothread and no extra stacks

Highly portable - the protothreads library is 100% pure C and no architecture specific assembly code

Can be used with or without an OS

Provides blocking wait without full multi-threading or stack-switching

Freely available under a BSD-like open source license

Example applications:

Memory constrained systems

Event-driven protocol stacks

Small embedded systems

Sensor network nodes

Portable C applications

For example usages, see the Examples page.

The protothreads library is released under an open source BSD-style license that freely allows for both non-commercial and commercial usage. The only requirement is that credit is given. Download the full source code here.

Protothreads were invented by Adam Dunkels with support from Oliver Schmidt <ol.sc@web.de>.