| 1 | // -*- Mode: C -*- |
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| 2 | // |
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| 3 | // Cforall Version 1.0.0 Copyright (C) 2022 University of Waterloo |
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| 4 | // |
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| 5 | // The contents of this file are covered under the licence agreement in the |
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| 6 | // file "LICENCE" distributed with Cforall. |
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| 7 | // |
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| 8 | // barrier.hfa -- simple barrier implemented using a monitor |
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| 9 | // |
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| 10 | // Author : Peter A. Buhr |
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| 11 | // Created On : Sun Nov 10 08:07:35 2024 |
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| 12 | // Last Modified By : Peter A. Buhr |
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| 13 | // Last Modified On : Sun Nov 10 08:11:55 2024 |
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| 14 | // Update Count : 3 |
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| 15 | // |
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| 16 | |
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| 17 | #pragma once |
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| 18 | |
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| 19 | #include <monitor.hfa> |
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| 20 | |
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| 21 | // Plan 9 inheritance does not work with monitors. Two monitor locks are created. |
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| 22 | |
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| 23 | monitor barrier { |
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| 24 | unsigned int group, arrivals; // group size, arrival counter |
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| 25 | condition c; // wait for group to form |
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| 26 | }; |
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| 27 | |
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| 28 | // Constructor |
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| 29 | void ?{}( barrier & b, unsigned group ) { |
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| 30 | b.group = b.arrivals = group; // count backwards |
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| 31 | } |
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| 32 | |
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| 33 | // Returns a value indicating the reverse order the threads arrived i.e. last thread returns 0 (and does not block) |
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| 34 | // last is an optional hook that is called by the last thread before unblocking the others. |
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| 35 | static inline unsigned block( barrier & mutex b, fptr_t last = (fptr_t)0 ) with( b ) { |
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| 36 | arrivals -= 1; // prefix decrement so last is 0 not 1 |
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| 37 | unsigned arrived = b.arrivals; // note arrival order |
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| 38 | if ( arrivals != 0 ) { // wait for group to form |
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| 39 | wait( b.c ); |
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| 40 | } else { // group formed |
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| 41 | if ( last ) last(); // safe to call |
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| 42 | signal_all( c ); // unblock group |
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| 43 | arrivals = group; // reset |
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| 44 | } // if |
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| 45 | return arrived; // return arrival order |
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| 46 | } |
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