116 lines
2.7 KiB
C++
116 lines
2.7 KiB
C++
/*
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* IXSelectInterruptEventFd.cpp
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* Author: Benjamin Sergeant
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* Copyright (c) 2018-2019 Machine Zone, Inc. All rights reserved.
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*/
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//
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// On Linux we use eventd to wake up select.
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//
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//
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// Linux/Android has a special type of virtual files. select(2) will react
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// when reading/writing to those files, unlike closing sockets.
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//
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// https://linux.die.net/man/2/eventfd
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// http://www.sourcexr.com/articles/2013/10/26/lightweight-inter-process-signaling-with-eventfd
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//
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// eventfd was added in Linux kernel 2.x, and our oldest Android (Kitkat 4.4)
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// is on Kernel 3.x
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//
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// cf Android/Kernel table here
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// https://android.stackexchange.com/questions/51651/which-android-runs-which-linux-kernel
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//
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// On macOS we use UNIX pipes to wake up select.
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//
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#include "IXSelectInterruptEventFd.h"
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#include <sys/eventfd.h>
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#include <unistd.h> // for write
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#include <string.h> // for strerror
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#include <fcntl.h>
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#include <errno.h>
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#include <sstream>
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namespace ix
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{
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SelectInterruptEventFd::SelectInterruptEventFd()
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{
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_eventfd = -1;
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}
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SelectInterruptEventFd::~SelectInterruptEventFd()
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{
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::close(_eventfd);
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}
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bool SelectInterruptEventFd::init(std::string& errorMsg)
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{
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// calling init twice is a programming error
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assert(_eventfd == -1);
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_eventfd = eventfd(0, 0);
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if (_eventfd < 0)
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{
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std::stringstream ss;
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ss << "SelectInterruptEventFd::init() failed in eventfd()"
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<< " : " << strerror(errno);
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errorMsg = ss.str();
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_eventfd = -1;
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return false;
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}
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if (fcntl(_eventfd, F_SETFL, O_NONBLOCK) == -1)
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{
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std::stringstream ss;
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ss << "SelectInterruptEventFd::init() failed in fcntl() call"
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<< " : " << strerror(errno);
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errorMsg = ss.str();
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_eventfd = -1;
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return false;
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}
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return true;
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}
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bool SelectInterruptEventFd::notify(uint64_t value)
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{
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int fd = _eventfd;
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if (fd == -1) return false;
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// we should write 8 bytes for an uint64_t
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return write(fd, &value, sizeof(value)) == 8;
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}
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// TODO: return max uint64_t for errors ?
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uint64_t SelectInterruptEventFd::read()
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{
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int fd = _eventfd;
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uint64_t value = 0;
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::read(fd, &value, sizeof(value));
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return value;
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}
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bool SelectInterruptEventFd::clear()
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{
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if (_eventfd == -1) return false;
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// 0 is a special value ; select will not wake up
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uint64_t value = 0;
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// we should write 8 bytes for an uint64_t
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return write(_eventfd, &value, sizeof(value)) == 8;
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}
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int SelectInterruptEventFd::getFd() const
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{
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return _eventfd;
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}
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}
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