Don't no if anyone else has noticed this: the pthread_cond_wait when
signalled does not lock the associated mutex again. Thus the expected
output of the attached program should be
create Test
start
bar mutex lock and wait
foo mutex lock
foo mutex lock and signal condition then sleep...
foo mutex unlock <------- Should
be here
bar mutex lock and wait released
bar mutex unlock
end
delete Test
But the actual output is:
create Test
start
bar mutex lock and wait
foo mutex lock
foo mutex lock and signal condition then sleep...
bar mutex lock and wait released
bar mutex unlock
foo mutex unlock <------- But here
instead
end
delete Test
Test program:
#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <pthread.h>
struct wait_cond {
wait_cond();
~wait_cond();
pthread_mutex_t _mutex;
pthread_cond_t _cond;
bool _status;
};
wait_cond::wait_cond()
: _status(false)
{
int status = ::pthread_mutex_init(&_mutex, 0);
if( 0 == status )
status = ::pthread_cond_init(&_cond, 0);
if( 0 == status )
_status = true;
assert(_status);
}
wait_cond::~wait_cond()
{
int status = ::pthread_cond_destroy(&_cond);
assert(0==status);
status = ::pthread_mutex_destroy(&_mutex);
assert(0==status);
}
struct Test
{
Test()
: _pwait_condition( new wait_cond )
{
::printf("create Test\n");
}
~Test()
{
::printf("delete Test\n");
delete _pwait_condition;
}
void *foo(void*)
{
int status = ::pthread_mutex_lock(&(_pwait_condition->_mutex));
::printf("foo mutex lock\n");
status = ::pthread_cond_signal(&(_pwait_condition->_cond));
::printf("foo mutex lock and signal condition then sleep...\n");
::sleep(1);
status = ::pthread_mutex_unlock(&(_pwait_condition->_mutex));
::printf("foo mutex unlock\n");
return 0;
};
void *bar(void*)
{
::pthread_mutex_lock(&(_pwait_condition->_mutex));
::printf("bar mutex lock and wait\n");
::pthread_cond_wait(&(_pwait_condition->_cond)
, &(_pwait_condition->_mutex));
::printf("bar mutex lock and wait released\n");
::pthread_mutex_unlock(&(_pwait_condition->_mutex));
::printf("bar mutex unlock\n");
return 0;
};
wait_cond *_pwait_condition;
};
void * foo(void* pv)
{
((Test *)pv)->foo(0);
}
void * bar(void* pv)
{
((Test *)pv)->bar(0);
}
int main(char** argc, int argv)
{
Test test;
pthread_t t1, t2;
::printf("start\n");
int status = ::pthread_create(&t2, 0, bar, &test);
assert(0==status);
status = ::pthread_create(&t1, 0, foo, &test);
assert(0==status);
::sleep(5);
::printf("end\n");
return 0;
}
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