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experimental code to use futexes instead of mutexes added to simple_semapthore_t

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This commit is contained in:
Martin Sustrik 2009-11-25 08:55:03 +01:00
parent c98fd6bc3f
commit 92aa9e94e2
1 changed files with 57 additions and 3 deletions
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60
src/simple_semaphore.hpp
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@ -23,7 +23,11 @@
#include "platform.hpp"
#include "err.hpp"
#if defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
#if 0 //defined ZMQ_HAVE_LINUX
#include <sys/syscall.h>
#include <unistd.h>
#include <linux/futex.h>
#elif defined ZMQ_HAVE_LINUX ||defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
#include <pthread.h>
#elif defined ZMQ_HAVE_WINDOWS
#include "windows.hpp"
@ -33,13 +37,63 @@
namespace zmq
{
// Simple semaphore. Only single thread may be waiting at any given time.
// Also, the semaphore may not be posted before the previous post
// was matched by corresponding wait and the waiting thread was
// released.
#if defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
#if 0 //defined ZMQ_HAVE_LINUX
// In theory, using private futexes should be more efficient on Linux
// platform than using mutexes. However, in uncontended cases of TCP
// transport on loopback interface we haven't seen any latency improvement.
// The code is commented out waiting for more thorough testing.
class simple_semaphore_t
{
public:
// Initialise the semaphore.
inline simple_semaphore_t () :
dummy (0)
{
}
// Destroy the semaphore.
inline ~simple_semaphore_t ()
{
}
// Wait for the semaphore.
inline void wait ()
{
int rc = syscall (SYS_futex, &dummy, (int) FUTEX_WAIT_PRIVATE,
(int) 0, NULL, NULL, (int) 0);
zmq_assert (rc == 0);
}
// Post the semaphore.
inline void post ()
{
while (true) {
int rc = syscall (SYS_futex, &dummy, (int) FUTEX_WAKE_PRIVATE,
(int) 1, NULL, NULL, (int) 0);
zmq_assert (rc != -1 && rc <= 1);
if (rc == 1)
break;
}
}
private:
int dummy;
// Disable copying of the object.
simple_semaphore_t (const simple_semaphore_t&);
void operator = (const simple_semaphore_t&);
};
#elif defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
// On platforms that allow for double locking of a mutex from the same
// thread, simple semaphore is implemented using mutex, as it is more