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POsegmentation fault appearing when program parameters are over a certain threshold
 

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  1. POsegmentation fault appearing when program parameters are over a certain threshold
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    <p>I'm writing this fairly big network simulator in C++. I've been regularly testing individual pieces as I was developing them, and after putting everything together it seems to work as long as the load I impose on the simulator is not too big (it's a P2P content distribution simulator, so the more different "contents" I introduce the more data transfers the simulator will have to handle). Anything above a certain threshold of the number of different contents being simulated will result in an abrupt SIGSEGV after several minutes of smooth running. I assumed there was a memory leak that was eventually becoming too large and messing things up, but a valgrind run with the parameters below the threshold terminated flawlessly. However, if I try to run the program with valgrind using a critical value for the content number, after a certain point I start to get memory access errors in functions that previously presented no problems:</p> <pre><code>==5987== Invalid read of size 8 ==5987== at 0x40524E: Scheduler::advanceClock() (Scheduler.cpp:38) ==5987== by 0x45BA73: TestRun::execute() (TestRun.cpp:73) ==5987== by 0x45522B: main (CDSim.cpp:131) ==5987== Address 0x2e63bc70 is 0 bytes inside a block of size 32 free'd ==5987== at 0x4C2A4BC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==5987== by 0x405487: Scheduler::advanceClock() (Scheduler.cpp:69) ==5987== by 0x45BA73: TestRun::execute() (TestRun.cpp:73) ==5987== by 0x45522B: main (CDSim.cpp:131) ==5987== ==5987== Invalid read of size 4 ==5987== at 0x40584E: Request::getSimTime() const (Event.hpp:45) ==5987== by 0x40525C: Scheduler::advanceClock() (Scheduler.cpp:38) ==5987== by 0x45BA73: TestRun::execute() (TestRun.cpp:73) ==5987== by 0x45522B: main (CDSim.cpp:131) ==5987== Address 0x2e63bc78 is 8 bytes inside a block of size 32 free'd ==5987== at 0x4C2A4BC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==5987== by 0x405487: Scheduler::advanceClock() (Scheduler.cpp:69) ==5987== by 0x45BA73: TestRun::execute() (TestRun.cpp:73) ==5987== by 0x45522B: main (CDSim.cpp:131) ==5987== </code></pre> <p>I know it might be hard to give an answer without seeing the whole code, but is there a "high-level" hint on what might be going on here? I don't understand why a function that seems to work normally suddenly starts misbehaving. Is there something obvious that I'm missing maybe?</p> <p>The incriminated line in the previous valgrind log is <code>if (nextEvent-&gt;getSimTime() &lt; this-&gt;getSimTime())</code> in the following block:</p> <pre><code>bool Scheduler::advanceClock() { if (pendingEvents.size() == 0) { std::cerr &lt;&lt; "WARNING: Scheduler::advanceClock() - Empty event queue before " "reaching the termination event" &lt;&lt; std::endl; return false; } const Event* nextEvent = pendingEvents.top(); // Check that the event is not scheduled in the past if (nextEvent-&gt;getSimTime() &lt; this-&gt;getSimTime()) { std::cerr &lt;&lt; "Scheduler::advanceClock() - Event scheduled in the past!" &lt;&lt; std::endl; std::cerr &lt;&lt; "Simulation time: " &lt;&lt; this-&gt;getSimTime() &lt;&lt; ", event time: " &lt;&lt; nextEvent-&gt;getSimTime() &lt;&lt; std::endl; exit(ERR_EVENT_IN_THE_PAST); } // Update the clock with the current event time (&gt;= previous time) this-&gt;setSimTime(nextEvent-&gt;getSimTime()); ... </code></pre> <p>where pendingEvents is a boost::heap::binomial_heap.</p>
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    1. USmanuhalo
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    1. COIt sounds likely that either `nextEvent` or `this` is an invalid pointer.
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      1. POsegmentation fault appearing when program parameters are over a certain threshold
      1. USOliver Charlesworth
    2. CO@OliCharlesworth: O RLY??? haha just kidding buddy. Sort of.
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      1. POsegmentation fault appearing when program parameters are over a certain threshold
      1. USDaniel
    3. CO@Daniel: I'm not sure it's possible to come to a more helpful conclusion than that with the information given here.
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      1. POsegmentation fault appearing when program parameters are over a certain threshold
      1. USOliver Charlesworth
 

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