Hello,
While porting a pthread-application from Linux to Cygwin I found
out that pthread_kill() behaves differently on Linux and Cygwin. It
looks like with Cygwin pthread_kill() sends a signal to the caller
thread instead of the thread specified in the argument list. I have
attached a test program and the output on Linux and on Cygwin with
this E-mail (in the included output you can see that I ran the test
program once on Cygwin, and four times on Linux).Regards, Bart Van Assche.
#include <cassert>
#include <cerrno>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <pthread.h>
#include <signal.h>
#include <sys/time.h>
#include <unistd.h>
#if defined NDEBUG
#define VERIFY(e) do { (e); } while (0)
#else
#define VERIFY(e) do { assert(e); } while (0)
#endif
static pthread_mutex_t s_Mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t s_Cond = PTHREAD_COND_INITIALIZER;
static void EmptySignalHandler(int)
{ }
static void* ThreadEntry(void*)
{
// Let the main thread know that the created thread started.
VERIFY(pthread_mutex_lock(&s_Mutex) == 0);
VERIFY(pthread_cond_signal(&s_Cond) == 0);
VERIFY(pthread_mutex_unlock(&s_Mutex) == 0);
// Wait until this thread is interrupted by pthread_kill().
timeval tvDelay = { 1000, 0 };
int const iResult = select(0, 0, 0, 0, &tvDelay);
assert(iResult < 0 && errno == EINTR);
return 0;
}
int main()
{
// Make sure that SIGALRM does not terminate the process.
struct sigaction SA;
memset(&SA, 0, sizeof(SA));
SA.sa_handler = &EmptySignalHandler;
sigemptyset(&SA.sa_mask);
sigaction(SIGALRM, &SA, 0);
// Create a thread.
pthread_t TID = 0;
VERIFY(pthread_mutex_lock(&s_Mutex) == 0);
VERIFY(pthread_create(&TID, 0, ThreadEntry, 0) == 0);
assert(TID != 0);
VERIFY(pthread_cond_wait(&s_Cond, &s_Mutex) == 0);
// Delay for 300 ms, in order to ensure that the thread is inside select()
// when pthread_kill() is called from this thread.
timeval tvDelay;
tvDelay.tv_sec = 0;
tvDelay.tv_usec = 300 * 1000;
VERIFY(select(0, 0, 0, 0, &tvDelay) == 0);
// Query the wall clock time before calling select().
timeval tvStart;
gettimeofday(&tvStart, 0);
// Interrupt any OS call the thread is doing by sending SIGALRM to it.
VERIFY(pthread_kill(TID, SIGALRM) == 0);
// Call select() with a timeout of 1s.
tvDelay.tv_sec = 1;
tvDelay.tv_usec = 0;
int const iResult = select(0, 0, 0, 0, &tvDelay);
// Again query the wall clock time.
timeval tvEnd;
gettimeofday(&tvEnd, 0);
timeval tvElapsed;
timersub(&tvEnd, &tvStart, &tvElapsed);
double const dElapsed = tvElapsed.tv_sec + tvElapsed.tv_usec * 1e-6;
printf("select() returned after %f s with result %d / errno = %d\n",
dElapsed, iResult, errno);
assert(iResult == 0);
// At least one second must have elapsed during the select() call.
assert(dElapsed >= 0.99);
VERIFY(pthread_join(TID, 0) == 0);
VERIFY(pthread_mutex_unlock(&s_Mutex) == 0);
return 0;
}
/*
Local variables:
compile-command: "g++ -Wall -W ptk.cpp -o ptk -lpthread"
End:
*/
select() returned after 0.999753 s with result 0 / errno = 0 select() returned after 0.999751 s with result 0 / errno = 0 select() returned after 0.999749 s with result 0 / errno = 0 select() returned after 1.000750 s with result 0 / errno = 0
select() returned after 0.000000 s with result -1 / errno = 4 assertion "iResult == 0" failed: file "ptk.cpp", line 76 Aborted (core dumped)
cygcheck.out
Description: Binary data
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