qemu-thread: add QemuSemaphore

The new thread pool will use semaphores instead of condition
variables, because QemuCond does not have qemu_cond_timedwait.
(I also like it more this way).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-thread-posix.c

@@ -17,6 +17,9 @@
 #include <signal.h>
 #include <stdint.h>
 #include <string.h>
+#include <limits.h>
+#include <unistd.h>
+#include <sys/time.h>
 #include "qemu-thread.h"
 
 static void error_exit(int err, const char *msg)
@@ -115,6 +118,83 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
         error_exit(err, __func__);
 }
 
+void qemu_sem_init(QemuSemaphore *sem, int init)
+{
+    int rc;
+
+    rc = sem_init(&sem->sem, 0, init);
+    if (rc < 0) {
+        error_exit(errno, __func__);
+    }
+}
+
+void qemu_sem_destroy(QemuSemaphore *sem)
+{
+    int rc;
+
+    rc = sem_destroy(&sem->sem);
+    if (rc < 0) {
+        error_exit(errno, __func__);
+    }
+}
+
+void qemu_sem_post(QemuSemaphore *sem)
+{
+    int rc;
+
+    rc = sem_post(&sem->sem);
+    if (rc < 0) {
+        error_exit(errno, __func__);
+    }
+}
+
+int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
+{
+    int rc;
+
+    if (ms <= 0) {
+        /* This is cheaper than sem_timedwait.  */
+        do {
+            rc = sem_trywait(&sem->sem);
+        } while (rc == -1 && errno == EINTR);
+        if (rc == -1 && errno == EAGAIN) {
+            return -1;
+        }
+    } else {
+        struct timeval tv;
+        struct timespec ts;
+        gettimeofday(&tv, NULL);
+        ts.tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
+        ts.tv_sec = tv.tv_sec + ms / 1000;
+        if (ts.tv_nsec >= 1000000000) {
+            ts.tv_sec++;
+            ts.tv_nsec -= 1000000000;
+        }
+        do {
+            rc = sem_timedwait(&sem->sem, &ts);
+        } while (rc == -1 && errno == EINTR);
+        if (rc == -1 && errno == ETIMEDOUT) {
+            return -1;
+        }
+    }
+    if (rc < 0) {
+        error_exit(errno, __func__);
+    }
+    return 0;
+}
+
+void qemu_sem_wait(QemuSemaphore *sem)
+{
+    int rc;
+
+    do {
+        rc = sem_wait(&sem->sem);
+    } while (rc == -1 && errno == EINTR);
+    if (rc < 0) {
+        error_exit(errno, __func__);
+    }
+}
+
 void qemu_thread_create(QemuThread *thread,
                        void *(*start_routine)(void*),
                        void *arg, int mode)