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c38b71146b
There is a race between the trace subject doing the buffer initialization and the monitor trying to iterate the buffer entries. If the monitor tries to iterate entries of an uninitialized buffer, it will read the very first entry twice. The monitor should therefore only start iteration when the buffer has been initialised. genodelabs/genode#4513
89 lines
2.2 KiB
C++
89 lines
2.2 KiB
C++
/*
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* \brief Wrapper for Trace::Buffer that adds some convenient functionality
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* \author Martin Stein
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* \date 2018-01-12
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*/
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/*
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* Copyright (C) 2018 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#ifndef _TRACE__TRACE_BUFFER_H_
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#define _TRACE__TRACE_BUFFER_H_
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/* Genode includes */
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#include <base/trace/buffer.h>
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/**
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* Wrapper for Trace::Buffer that adds some convenient functionality
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*/
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class Trace_buffer
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{
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private:
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using Entry = Genode::Trace::Buffer::Entry;
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Genode::Trace::Buffer &_buffer;
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Entry _curr { Entry::invalid() };
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unsigned long long _lost_count { 0 };
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public:
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Trace_buffer(Genode::Trace::Buffer &buffer) : _buffer(buffer) { }
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/**
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* Call functor for each entry that wasn't yet processed
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*/
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template <typename FUNC>
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void for_each_new_entry(FUNC && functor, bool update = true)
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{
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using namespace Genode;
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if (!_buffer.initialized())
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return;
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bool lost = _buffer.lost_entries() != _lost_count;
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if (lost) {
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warning("lost ", _buffer.lost_entries() - _lost_count,
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", entries; you might want to raise buffer size");
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_lost_count = (unsigned)_buffer.lost_entries();
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}
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Entry entry { _curr };
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/**
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* Iterate over all entries that were not processed yet.
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*
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* A note on terminology: The head of the buffer marks the write
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* position. The first entry is the one that starts at the lowest
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* memory address. The next entry returns an invalid entry
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* if the 'last' entry of the buffer (highest address) was reached.
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*/
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for (; !entry.head(); entry = _buffer.next(entry)) {
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/* continue at first entry if we hit the end of the buffer */
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if (entry.last())
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entry = _buffer.first();
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/* skip empty entries */
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if (entry.empty())
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continue;
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/* functor may return false to continue processing later on */
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if (!functor(entry))
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break;
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}
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/* remember the next to be processed entry in _curr */
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if (update) _curr = entry;
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}
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void * address() const { return &_buffer; }
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bool empty() const { return _curr.head(); }
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};
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#endif /* _TRACE__TRACE_BUFFER_H_ */
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