Date: Tue, 10 Apr 2012 20:52:13 +0100 From: Ben Short <ben@benshort.co.uk> To: freebsd-questions@freebsd.org Subject: Re: Using kqueue with 2 threads Message-ID: <CAOiKr=tV7GioR4gVnXQmWx=HU4yzpzubAdsiycJHZcxTGJ2FKw@mail.gmail.com> In-Reply-To: <CAOiKr=t3V=MWCc6Z_%2BskZYkS-jrXwXUiOkuOk7N_sBCaKWMZxQ@mail.gmail.com> References: <CAOiKr=t3V=MWCc6Z_%2BskZYkS-jrXwXUiOkuOk7N_sBCaKWMZxQ@mail.gmail.com>
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I have put together the following example and can still see the problem.
Once the file is written to extended is printed every second. If I remove
the sleep then it prints a whole lot more. So it seems that the call to
kevent in the worker_thread method blocks until the file is written to then
it returns the same event straight away on every call.
Is this expected? Am I meant to clear the event some how?
#include <cstdlib>
#include <iostream>
#include <sys/stat.h>
#include <sys/errno.h>
#include <iostream>
#include <fstream>
#include <cstring>
#include <stdio.h>
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include <stdio.h>
#include <fcntl.h>
using namespace std;
struct wrapper {
int kq;
};
static void* worker_thread(void* obj) {
int kq = ((wrapper*)obj)->kq;
std::cerr << "Started worker" << std::endl;
struct kevent ke;
int i;
while ( 1 ) {
memset(&ke, 0x00, sizeof(ke));
i = kevent(kq, NULL, 0, &ke, 1, NULL);
if ( i == -1 ) {
std::cerr << "kqueue produced error: " << strerror(i) <<
std::endl;
continue; // todo is this the best thing todo?
} else if ( i == 0 ) {
std::cerr << "kqueue time limit expired" << std::endl;
continue;
}
if ( ke.filter == EVFILT_VNODE ) {
if ( ke.fflags & NOTE_DELETE ) {
std::cerr << "delete" << std::endl;
break;
} else if ( ke.fflags & NOTE_RENAME ) {
std::cerr << "rename" << std::endl;
} else if ( ke.fflags & NOTE_EXTEND ) {
std::cerr << "extended" << std::endl;
} else {
std::cerr << "some other fflags" << std::endl;
}
} else {
std::cerr << "some other filter" << std::endl;
}
sleep(1);
}
std::cerr << "Shutting down worker" << std::endl;
return 0;
}
void writeToFile(std::string fileName, std::string key, std::string value) {
std::fstream registryEntry;
registryEntry.exceptions(std::ifstream::failbit |
std::ifstream::badbit);
try {
registryEntry.open(fileName.c_str(), std::ios::out |
std::ios::binary);
size_t keyLength = key.length();
registryEntry.write((char*)&keyLength, sizeof(size_t));
registryEntry.write(key.c_str(), key.length());
size_t valueLength = value.length();
registryEntry.write((char*)&valueLength, sizeof(size_t));
registryEntry.write(value.c_str(), value.length());
std::cout << "Set entry with key: " << key << std::endl;
} catch (std::ifstream::failure e) {
// todo throw exception
std::cerr << "Failed to set registry entry. Error: " << e.what() <<
std::endl;
}
registryEntry.close();
}
void test2() {
int kq = kqueue();
if ( kq == -1 ) {
std::cerr << "Failed to create kqueue. Error: " << strerror(errno)
<< std::endl;
return;
}
pthread_t worker;
wrapper wrap;
wrap.kq = kq;
if ( pthread_create(&worker, 0, worker_thread, &wrap) != 0 ) {
std::cerr << "Failed to create listener thread. Error: " <<
strerror(errno) << std::endl;
}
int fd = open("/tmp/tt", O_RDONLY);
if ( fd == -1 ) {
std::cerr << "Failed to open file: " << "/tmp/tt" << " Error: " <<
strerror(errno) << std::endl;
// todo throw exception
}
struct kevent ke;
EV_SET(&ke, fd, EVFILT_VNODE, EV_ADD, NOTE_DELETE | NOTE_RENAME |
NOTE_EXTEND, 0, NULL);
if (kevent(kq, &ke, 1, NULL, 0, NULL) == -1) {
std::cerr << "kevent produced error: " << strerror(errno) <<
std::endl;
}
sleep(1);
writeToFile("/tmp/tt", "key1", "value1");
sleep(5);
}
/*
*
*/
int main(int argc, char** argv) {
test2();
return 0;
}
On 10 April 2012 15:25, Ben Short <ben@benshort.co.uk> wrote:
> Hi,
>
> I'm trying to use a kqueue to listen for VNODE events on a worker thread.
> I want new events to be registered with the kqueue by a separate thread.
>
> I have been referring to this example [URL="
> http://doc.geoffgarside.co.uk/kqueue/file.html"]
> http://doc.geoffgarside.co.uk/kqueue/file.html[/URL]
>
> Here are the relevant parts of code as it is at the moment.
>
> In my worker thread:
>
> [CODE]std::cerr << "Started worker" << std::endl;
>
> struct kevent ke;
> int i;
>
> while ( !mStopRequested ) {
>
> memset(&ke, 0x00, sizeof(kevent));
>
> i = kevent(kq, NULL, 0, &ke, 1, NULL);
> if ( i == -1 ) {
> std::cerr << "kqueue produced error: " << strerror(i) <<
> std::endl;
> continue; // todo is this the best thing todo?
> }
>
> std::cerr << "Beep: " << i << std::endl;
>
> }
>
> std::cerr << "Shutting down worker" << std::endl;[/CODE]
>
> Other thread
>
> [CODE]int fd = open(fileName.c_str(), O_RDONLY);
> if ( fd == -1 ) {
> std::cerr << "Failed to open file: " << fileName << " Error: " <<
> strerror(errno) << std::endl;
> // todo throw exception
> }
>
> struct kevent ke;
>
> EV_SET(&ke, fd, EVFILT_VNODE, EV_ADD, NOTE_DELETE | NOTE_RENAME |
> NOTE_EXTEND, 0, NULL);
>
> if (kevent(kq, &ke, 1, NULL, 0, NULL) == -1) {
> std::cerr << "kevent produced error: " << strerror(errno) <<
> std::endl;
> }[/CODE]
>
>
> When I run my code the kevent call in the worker code doesn't block at
> all. Any ideas what I'm missing? or if what I want to do is even possible?
>
> Ben
>
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