[v2,1/3] sem-posix: remove the posix semaphore support

Commit Message

Denis V. Lunev" via Feb. 22, 2022, 9:05 a.m. UTC

POSIX specifies an absolute time for sem_timedwait(), it would be
affected if the system time is changing, but there is not a relative
time or monotonic clock version of sem_timedwait, so we cannot gain
from POSIX semaphore any more.

An alternative way is to use sem_trywait + usleep, maybe we can
remove CONFIG_SEM_TIMEDWAIT in this way? No, because some systems
(e.g. mac os) mark the sem_xxx API as deprecated.

So maybe remove the usage of POSIX semaphore and turn to use the
pthread variant for all systems looks better.

Signed-off-by: Longpeng(Mike) <[e-mail]>
---
 include/qemu/thread-posix.h |  4 ----
 meson.build                 |  1 -
 util/qemu-thread-posix.c    | 54 ---------------------------------------------
 3 files changed, 59 deletions(-)

Patch

diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index b792e6e..5466608 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -27,13 +27,9 @@  struct QemuCond {
 };
 
 struct QemuSemaphore {
-#ifndef CONFIG_SEM_TIMEDWAIT
     pthread_mutex_t lock;
     pthread_cond_t cond;
     unsigned int count;
-#else
-    sem_t sem;
-#endif
     bool initialized;
 };
 
diff --git a/meson.build b/meson.build
index 762d7ce..3ccb110 100644
--- a/meson.build
+++ b/meson.build
@@ -1557,7 +1557,6 @@  config_host_data.set('CONFIG_POSIX_FALLOCATE', cc.has_function('posix_fallocate'
 config_host_data.set('CONFIG_POSIX_MEMALIGN', cc.has_function('posix_memalign'))
 config_host_data.set('CONFIG_PPOLL', cc.has_function('ppoll'))
 config_host_data.set('CONFIG_PREADV', cc.has_function('preadv', prefix: '#include <sys/uio.h>'))
-config_host_data.set('CONFIG_SEM_TIMEDWAIT', cc.has_function('sem_timedwait', dependencies: threads))
 config_host_data.set('CONFIG_SENDFILE', cc.has_function('sendfile'))
 config_host_data.set('CONFIG_SETNS', cc.has_function('setns') and cc.has_function('unshare'))
 config_host_data.set('CONFIG_SYNCFS', cc.has_function('syncfs'))
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index e1225b6..1ad2503 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -219,7 +219,6 @@  void qemu_sem_init(QemuSemaphore *sem, int init)
 {
     int rc;
 
-#ifndef CONFIG_SEM_TIMEDWAIT
     rc = pthread_mutex_init(&sem->lock, NULL);
     if (rc != 0) {
         error_exit(rc, __func__);
@@ -232,12 +231,6 @@  void qemu_sem_init(QemuSemaphore *sem, int init)
         error_exit(EINVAL, __func__);
     }
     sem->count = init;
-#else
-    rc = sem_init(&sem->sem, 0, init);
-    if (rc < 0) {
-        error_exit(errno, __func__);
-    }
-#endif
     sem->initialized = true;
 }
 
@@ -247,7 +240,6 @@  void qemu_sem_destroy(QemuSemaphore *sem)
 
     assert(sem->initialized);
     sem->initialized = false;
-#ifndef CONFIG_SEM_TIMEDWAIT
     rc = pthread_cond_destroy(&sem->cond);
     if (rc < 0) {
         error_exit(rc, __func__);
@@ -256,12 +248,6 @@  void qemu_sem_destroy(QemuSemaphore *sem)
     if (rc < 0) {
         error_exit(rc, __func__);
     }
-#else
-    rc = sem_destroy(&sem->sem);
-    if (rc < 0) {
-        error_exit(errno, __func__);
-    }
-#endif
 }
 
 void qemu_sem_post(QemuSemaphore *sem)
@@ -269,7 +255,6 @@  void qemu_sem_post(QemuSemaphore *sem)
     int rc;
 
     assert(sem->initialized);
-#ifndef CONFIG_SEM_TIMEDWAIT
     pthread_mutex_lock(&sem->lock);
     if (sem->count == UINT_MAX) {
         rc = EINVAL;
@@ -281,12 +266,6 @@  void qemu_sem_post(QemuSemaphore *sem)
     if (rc != 0) {
         error_exit(rc, __func__);
     }
-#else
-    rc = sem_post(&sem->sem);
-    if (rc < 0) {
-        error_exit(errno, __func__);
-    }
-#endif
 }
 
 int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
@@ -295,7 +274,6 @@  int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
     struct timespec ts;
 
     assert(sem->initialized);
-#ifndef CONFIG_SEM_TIMEDWAIT
     rc = 0;
     compute_abs_deadline(&ts, ms);
     pthread_mutex_lock(&sem->lock);
@@ -313,29 +291,6 @@  int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
     }
     pthread_mutex_unlock(&sem->lock);
     return (rc == ETIMEDOUT ? -1 : 0);
-#else
-    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 {
-        compute_abs_deadline(&ts, ms);
-        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;
-#endif
 }
 
 void qemu_sem_wait(QemuSemaphore *sem)
@@ -343,7 +298,6 @@  void qemu_sem_wait(QemuSemaphore *sem)
     int rc;
 
     assert(sem->initialized);
-#ifndef CONFIG_SEM_TIMEDWAIT
     pthread_mutex_lock(&sem->lock);
     while (sem->count == 0) {
         rc = pthread_cond_wait(&sem->cond, &sem->lock);
@@ -353,14 +307,6 @@  void qemu_sem_wait(QemuSemaphore *sem)
     }
     --sem->count;
     pthread_mutex_unlock(&sem->lock);
-#else
-    do {
-        rc = sem_wait(&sem->sem);
-    } while (rc == -1 && errno == EINTR);
-    if (rc < 0) {
-        error_exit(errno, __func__);
-    }
-#endif
 }
 
 #ifdef __linux__