[vlc-devel] [PATCH] android: threads support
Rémi Denis-Courmont
remi at remlab.net
Sat Oct 6 15:10:48 CEST 2012
__threLe samedi 6 octobre 2012 15:31:31, Rafaël Carré a écrit :
> ---
> This version uses __thread rather than pthread_getspecific()
Nice.
> Tested on gcc 4.4.3.
> This removes the need for constructor/destructor functions, as
> we can use vlc_threads_setup().
>
> thread->lock is not used with condition variables anymore and becomes a
> valid mutex during the whole duration of the thread (until vlc_join())
> used to protect the condition variable (needed to make pthread_cond_*wait()
> cancellation points).
>
> The lock is only contended once when vlc_cancel(thread) is called.
>
> include/vlc_threads.h | 26 +-
> src/Makefile.am | 2 +-
> src/android/thread.c | 734
> +++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 758
> insertions(+), 4 deletions(-)
> create mode 100644 src/android/thread.c
>
> diff --git a/include/vlc_threads.h b/include/vlc_threads.h
> index cc0e8b1..20b967a 100644
> --- a/include/vlc_threads.h
> +++ b/include/vlc_threads.h
> @@ -42,6 +42,16 @@
>
> # define pthread_sigmask sigprocmask
>
> +#elif defined( __ANDROID__ ) /* pthreads subset without
> pthread_cancel() */ +
> +# define LIBVLC_USE_PTHREAD 1
> +# define LIBVLC_NEED_SEMAPHORE
> +# define LIBVLC_NEED_RWLOCK
> +
> +# include <unistd.h> /* _POSIX_SPIN_LOCKS */
> +# include <pthread.h>
> +# include <poll.h>
> +
> #else /* pthreads (like Linux &
> BSD) */ # define LIBVLC_USE_PTHREAD 1
> # define LIBVLC_USE_PTHREAD_CANCEL 1
> @@ -117,19 +127,27 @@
>
> **************************************************************************
> ***/
>
> #if defined (LIBVLC_USE_PTHREAD)
> +# ifdef LIBVLC_USE_PTHREAD_CANCEL
> typedef pthread_t vlc_thread_t;
> +# else
> +typedef struct vlc_thread *vlc_thread_t;
> +# endif
> typedef pthread_mutex_t vlc_mutex_t;
> #define VLC_STATIC_MUTEX PTHREAD_MUTEX_INITIALIZER
> typedef pthread_cond_t vlc_cond_t;
> #define VLC_STATIC_COND PTHREAD_COND_INITIALIZER
> +
> +# ifndef LIBVLC_NEED_RWLOCK
> typedef pthread_rwlock_t vlc_rwlock_t;
> -#define VLC_STATIC_RWLOCK PTHREAD_RWLOCK_INITIALIZER
> +# define VLC_STATIC_RWLOCK PTHREAD_RWLOCK_INITIALIZER
> +# endif
> +
> typedef pthread_key_t vlc_threadvar_t;
> typedef struct vlc_timer *vlc_timer_t;
>
> #if defined (__APPLE__)
> typedef semaphore_t vlc_sem_t;
> -#else
> +#elif !defined (LIBVLC_NEED_SEMAPHORE)
> typedef sem_t vlc_sem_t;
> #endif
Android does not belong here. There's hardly any common code.
> diff --git a/src/android/thread.c b/src/android/thread.c
> new file mode 100644
> index 0000000..61b78df
> --- /dev/null
> +++ b/src/android/thread.c
> @@ -0,0 +1,734 @@
> +/*************************************************************************
> **** + * thread.c : android pthread back-end for LibVLC
> +
> **************************************************************************
> *** + * Copyright (C) 1999-2012 VLC authors and VideoLAN
> + *
> + * Authors: Jean-Marc Dressler <polux at via.ecp.fr>
> + * Samuel Hocevar <sam at zoy.org>
> + * Gildas Bazin <gbazin at netcourrier.com>
> + * Clément Sténac
> + * Rémi Denis-Courmont
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU Lesser General Public License as published
> by + * the Free Software Foundation; either version 2.1 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> License + * along with this program; if not, write to the Free Software
> Foundation, + * Inc., 51 Franklin Street, Fifth Floor, Boston MA
> 02110-1301, USA. +
> **************************************************************************
> ***/ +
> +#ifdef HAVE_CONFIG_H
> +# include "config.h"
> +#endif
> +
> +#include <vlc_common.h>
> +#include <vlc_atomic.h>
> +
> +#include "libvlc.h"
> +#include <stdarg.h>
I could not find why this one was needed.
> +#include <signal.h>
> +#include <errno.h>
> +#include <time.h>
> +
> +#include <sys/types.h>
> +#include <unistd.h> /* fsync() */
> +#include <pthread.h>
> +#include <sched.h>
> +
> +#include <android/log.h>
> +#include <sys/syscall.h> /* __NR_gettid */
> +
> +/si* FIXME: Android 4.x has a monotonic clock */
> +# warning Monotonic clock not available. Expect timing issues.
To be precise, it is available since Android 1.6.
> +
> +#define vlc_assert(x) do { \
> + if (unlikely(!x)) { \
> + __android_log_print(ANDROID_LOG_ERROR, "vlc", "assert failed %s:%d:
> %s", \ + __FILE__, __LINE__, #x \
> + ); \
> + abort(); \
> + } \
> +} while(0)
> +
> +static struct timespec mtime_to_ts (mtime_t date)
> +{
> + lldiv_t d = lldiv (date, CLOCK_FREQ);
> + struct timespec ts = { d.quot, d.rem * (1000000000 / CLOCK_FREQ) };
> +
> + return ts;
> +}
> +
> +#ifndef NDEBUG
> +/*
> + * Reports a fatal error from the threading layer, for debugging purposes.
> + */
Stil lot of duplicated documentation. It is only a matter of time before it
becomes stale.
> +static void
> +vlc_thread_fatal (const char *action, int error,
> + const char *function, const char *file, unsigned line)
> +{
> + __android_log_print(ANDROID_LOG_ERROR, "vlc",
> + "LibVLC fatal error %s (%d) in thread %d ",
> + action, error, syscall (__NR_gettid));
> + fprintf (stderr, "at %s:%u in %s\n", file, line, function);
> + fflush (stderr); /* needed before switch to low-level I/O */
> + fsync (2);
> +
> + /* Sometimes strerror_r() crashes too, so make sure we print an error
> + * message before we invoke it */
Really?
> + char buf[1000];
> + const char *msg;
> +
> + switch (strerror_r (error, buf, sizeof (buf)))
> + {
> + case 0:
> + msg = buf;
> + break;
> + case ERANGE: /* should never happen */
> + msg = "unknown (too big to display)";
> + break;
> + default:
> + msg = "unknown (invalid error number)";
> + break;
> + }
> + fprintf (stderr, " Error message: %s\n", msg);
> + fflush (stderr);
> +
> + abort ();
> +}
> +
> +# define VLC_THREAD_ASSERT( action ) \
> + if (unlikely(val)) \
> + vlc_thread_fatal (action, val, __func__, __FILE__, __LINE__)
> +#else
> +# define VLC_THREAD_ASSERT( action ) ((void)val)
> +#endif
> +
> +/*
> + * Initializes a fast mutex.
> + */
> +void vlc_mutex_init( vlc_mutex_t *p_mutex )
> +{
> + pthread_mutexattr_t attr;
> +
> + pthread_mutexattr_init (&attr);
> +#ifdef NDEBUG
> + pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_DEFAULT);
> +#else
> + pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ERRORCHECK);
> +#endif
> + pthread_mutex_init (p_mutex, &attr);
> + pthread_mutexattr_destroy( &attr );
> +}
> +
> +/*
> + * Initializes a recursive mutex.
> + * \warning This is strongly discouraged. Please use normal mutexes.
> + */
> +void vlc_mutex_init_recursive( vlc_mutex_t *p_mutex )
> +{
> + pthread_mutexattr_t attr;
> +
> + pthread_mutexattr_init (&attr);
> + pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_RECURSIVE);
> + pthread_mutex_init (p_mutex, &attr);
> + pthread_mutexattr_destroy( &attr );
> +}
> +
> +
> +/*
> + * Destroys a mutex. The mutex must not be locked.
> + *
> + * @param p_mutex mutex to destroy
> + * @return always succeeds
> + */
> +void vlc_mutex_destroy (vlc_mutex_t *p_mutex)
> +{
> + int val = pthread_mutex_destroy( p_mutex );
> + VLC_THREAD_ASSERT ("destroying mutex");
> +}
> +
> +#ifndef NDEBUG
> +/*
> + * Asserts that a mutex is locked by the calling thread.
> + */
> +void vlc_assert_locked (vlc_mutex_t *p_mutex)
> +{
> + vlc_assert (pthread_mutex_lock (p_mutex) == EDEADLK);
> +}
> +#endif
> +
> +/*
> + * Acquires a mutex. If needed, waits for any other thread to release it.
> + * Beware of deadlocks when locking multiple mutexes at the same time,
> + * or when using mutexes from callbacks.
> + * This function is not a cancellation-point.
> + *
> + * @param p_mutex mutex initialized with vlc_mutex_init() or
> + * vlc_mutex_init_recursive()
> + */
> +void vlc_mutex_lock (vlc_mutex_t *p_mutex)
> +{
> + int val = pthread_mutex_lock( p_mutex );
> + VLC_THREAD_ASSERT ("locking mutex");
> +}
> +
> +/*
> + * Acquires a mutex if and only if it is not currently held by another
> thread. + * This function never sleeps and can be used in delay-critical
> code paths. + * This function is not a cancellation-point.
> + *
> + * <b>Beware</b>: If this function fails, then the mutex is held... by
> another + * thread. The calling thread must deal with the error
> appropriately. That + * typically implies postponing the operations that
> would have required the + * mutex. If the thread cannot defer those
> operations, then it must use + * vlc_mutex_lock(). If in doubt, use
> vlc_mutex_lock() instead.
> + *
> + * @param p_mutex mutex initialized with vlc_mutex_init() or
> + * vlc_mutex_init_recursive()
> + * @return 0 if the mutex could be acquired, an error code otherwise.
> + */
> +int vlc_mutex_trylock (vlc_mutex_t *p_mutex)
> +{
> + int val = pthread_mutex_trylock( p_mutex );
> +
> + if (val != EBUSY)
> + VLC_THREAD_ASSERT ("locking mutex");
> + return val;
> +}
> +
> +/*
> + * Releases a mutex (or crashes if the mutex is not locked by the caller).
> + * @param p_mutex mutex locked with vlc_mutex_lock().
> + */
> +void vlc_mutex_unlock (vlc_mutex_t *p_mutex)
> +{
> + int val = pthread_mutex_unlock( p_mutex );
> + VLC_THREAD_ASSERT ("unlocking mutex");
> +}
> +
> +struct vlc_thread
> +{
> + pthread_t thread;
> + pthread_cond_t *cond; /// Non-null if thread waiting on cond
> + vlc_mutex_t lock ; /// Protects cond
> +
> + void *(*entry)(void*);
> + void *data;
> +
> + bool killable;
> + bool killed;
> + bool finished;
> +};
> +
> +static __thread struct vlc_thread *thread = NULL;
> +
> +void vlc_threads_setup (libvlc_int_t *p_libvlc)
> +{
> + static struct vlc_thread main_thread = {
> + .cond = NULL,
> + .lock = VLC_STATIC_MUTEX,
> + .killable = false,
> + .killed = false,
> + .finished = false,
> + };
> +
> + thread = &main_thread;
> + thread->thread = pthread_self();
> +}
I don't understand why this is needed.
Also, it won't work with multiple instances.
> +
> +static void *andro_Thread(void *data)
> +{
> + thread = data;
> + void *ret = thread->entry(thread->data);
> + thread->finished = true;
This datum will become visible to other threads only after pthread_join()
succeeds, and thus is intrinsically useless.
> + return ret;
> +}
> +
> +/*
> + * Initializes a condition variable.
> + */
> +void vlc_cond_init (vlc_cond_t *p_condvar)
> +{
> + if (unlikely(pthread_cond_init (p_condvar, NULL)))
> + abort ();
> +}
> +
> +/*
> + * Initializes a condition variable.
> + * Contrary to vlc_cond_init(), the wall clock will be used as a reference
> for + * the vlc_cond_timedwait() time-out parameter.
> + */
> +void vlc_cond_init_daytime (vlc_cond_t *p_condvar)
> +{
> + vlc_cond_init(p_condvar);
> +}
> +
> +/*
> + * Destroys a condition variable. No threads shall be waiting or signaling
> the + * condition.
> + * @param p_condvar condition variable to destroy
> + */
> +void vlc_cond_destroy (vlc_cond_t *p_condvar)
> +{
> + int val = pthread_cond_destroy( p_condvar );
> + VLC_THREAD_ASSERT ("destroying condition");
> +}
> +
> +/*
> + * Wakes up one thread waiting on a condition variable, if any.
> + * @param p_condvar condition variable
> + */
> +void vlc_cond_signal (vlc_cond_t *p_condvar)
> +{
> + int val = pthread_cond_signal( p_condvar );
> + VLC_THREAD_ASSERT ("signaling condition variable");
> +}
> +
> +/*
> + * Wakes up all threads (if any) waiting on a condition variable.
> + * @param p_cond condition variable
> + */
> +void vlc_cond_broadcast (vlc_cond_t *p_condvar)
> +{
> + pthread_cond_broadcast (p_condvar);
> +}
> +
> +/*
> + * Waits for a condition variable. The calling thread will be suspended
> until + * another thread calls vlc_cond_signal() or vlc_cond_broadcast()
> on the same + * condition variable, the thread is cancelled with
> vlc_cancel(), or the + * system causes a "spurious" unsolicited wake-up.
> + *
> + * A mutex is needed to wait on a condition variable. It must <b>not</b>
> be + * a recursive mutex. Although it is possible to use the same mutex
> for + * multiple condition, it is not valid to use different mutexes for
> the same + * condition variable at the same time from different threads.
> + *
> + * In case of thread cancellation, the mutex is always locked before
> + * cancellation proceeds.
> + *
> + * The canonical way to use a condition variable to wait for event foobar
> is: + @code
> + vlc_mutex_lock (&lock);
> + mutex_cleanup_push (&lock); // release the mutex in case of
> cancellation +
> + while (!foobar)
> + vlc_cond_wait (&wait, &lock);
> +
> + --- foobar is now true, do something about it here --
> +
> + vlc_cleanup_run (); // release the mutex
> + @endcode
> + *
> + * @param p_condvar condition variable to wait on
> + * @param p_mutex mutex which is unlocked while waiting,
> + * then locked again when waking up.
> + * @param deadline <b>absolute</b> timeout
> + */
> +void vlc_cond_wait (vlc_cond_t *p_condvar, vlc_mutex_t *p_mutex)
> +{
> + if (thread) {
> + vlc_testcancel();
> + vlc_mutex_lock(&thread->lock);
> + thread->cond = p_condvar;
> + vlc_mutex_unlock(&thread->lock);
> + }
> +
> + int val = pthread_cond_wait( p_condvar, p_mutex );
> +
> + if (thread) {
> + vlc_mutex_lock(&thread->lock);
> + thread->cond = NULL;
> + vlc_mutex_unlock(&thread->lock);
> + vlc_testcancel();
> + }
> +
> + VLC_THREAD_ASSERT ("waiting on condition");
> +}
> +
> +/*
> + * Waits for a condition variable up to a certain date.
> + * This works like vlc_cond_wait(), except for the additional time-out.
> + *
> + * If the variable was initialized with vlc_cond_init(), the timeout has
> the + * same arbitrary origin as mdate(). If the variable was initialized
> with + * vlc_cond_init_daytime(), the timeout is expressed from the Unix
> epoch. + *
> + * @param p_condvar condition variable to wait on
> + * @param p_mutex mutex which is unlocked while waiting,
> + * then locked again when waking up.
> + * @param deadline <b>absolute</b> timeout
> + *
> + * @return 0 if the condition was signaled, an error code in case of
> timeout. + */
> +int vlc_cond_timedwait (vlc_cond_t *p_condvar, vlc_mutex_t *p_mutex,
> + mtime_t deadline)
> +{
> + struct timespec ts = mtime_to_ts (deadline);
> +
> + if (thread) {
> + vlc_testcancel();
> + vlc_mutex_lock(&thread->lock);
> + thread->cond = p_condvar;
> + vlc_mutex_unlock(&thread->lock);
> + }
> +
> + int val = pthread_cond_timedwait (p_condvar, p_mutex, &ts);
> + if (val != ETIMEDOUT)
> + VLC_THREAD_ASSERT ("timed-waiting on condition");
> +
> + if (thread) {
> + vlc_mutex_lock(&thread->lock);
> + thread->cond = NULL;
> + vlc_mutex_unlock(&thread->lock);
> + vlc_testcancel();
> + }
> +
> + return val;
> +}
> +
> +/*
> + * Allocates a thread-specific variable.
> + * @param key where to store the thread-specific variable handle
> + * @param destr a destruction callback. It is called whenever a thread
> exits + * and the thread-specific variable has a non-NULL value.
> + * @return 0 on success, a system error code otherwise. This function can
> + * actually fail because there is a fixed limit on the number of
> + * thread-specific variable in a process on most systems.
> + */
> +int vlc_threadvar_create (vlc_threadvar_t *key, void (*destr) (void *))
> +{
> + return pthread_key_create (key, destr);
> +}
> +
> +void vlc_threadvar_delete (vlc_threadvar_t *p_tls)
> +{
> + pthread_key_delete (*p_tls);
> +}
> +
> +/*
> + * Sets a thread-specific variable.
> + * @param key thread-local variable key (created with
> vlc_threadvar_create()) + * @param value new value for the variable for
> the calling thread + * @return 0 on success, a system error code
> otherwise.
> + */
> +int vlc_threadvar_set (vlc_threadvar_t key, void *value)
> +{
> + return pthread_setspecific (key, value);
> +}
> +
> +/*
> + * Gets the value of a thread-local variable for the calling thread.
> + * This function cannot fail.
> + * @return the value associated with the given variable for the calling
> + * or NULL if there is no value.
> + */
> +void *vlc_threadvar_get (vlc_threadvar_t key)
> +{
> + return pthread_getspecific (key);
> +}
> +
> +static int vlc_clone_attr (vlc_thread_t *th, pthread_attr_t *attr,
> + void *(*entry) (void *), void *data, int
> priority) +{
> + int ret;
> +
> + /*
> + * If the LibVLC caller wants to handle some signals by itself, it
> should + * block these before whenever invoking LibVLC. And it must
> obviously not + * start the VLC signals interface plugin.
> + *
> + * LibVLC will normally ignore any interruption caused by an
> asynchronous + * signal during a system call. But there may well be
> some buggy cases + * where it fails to handle EINTR (bug reports
> welcome). Some underlying + * libraries might also not handle EINTR
> properly.
> + */
> + sigset_t oldset;
> + {
> + sigset_t set;
> + sigemptyset (&set);
> + sigdelset (&set, SIGHUP);
> + sigaddset (&set, SIGINT);
> + sigaddset (&set, SIGQUIT);
> + sigaddset (&set, SIGTERM);
> +
> + sigaddset (&set, SIGPIPE); /* We don't want this one, really! */
> + pthread_sigmask (SIG_BLOCK, &set, &oldset);
> + }
> +
> + (void) priority;
> +
> +#define VLC_STACKSIZE (128 * sizeof (void *) * 1024)
> +
> +#ifdef VLC_STACKSIZE
> + ret = pthread_attr_setstacksize (attr, VLC_STACKSIZE);
> + vlc_assert (ret == 0); /* fails iif VLC_STACKSIZE is invalid */
> +#endif
> +
> + vlc_thread_t thread = malloc (sizeof (*thread));
> + if (unlikely(thread == NULL))
> + return ENOMEM;
This seems to constitute a memory leak if the thread is detached.
> +
> + thread->killable = true;
> + thread->killed = false;
> + thread->finished = false,
> + thread->cond = NULL;
> + thread->entry = entry;
> + thread->data = data;
> + vlc_mutex_init(&thread->lock);
This lock seems to be leaked if the thread is detached. This is not so
important since futexes are just memory.
> +
> + *th = thread;
> + ret = pthread_create (&thread->thread, attr, andro_Thread, thread);
> +
> + pthread_sigmask (SIG_SETMASK, &oldset, NULL);
> + pthread_attr_destroy (attr);
> + return ret;
> +}
> +
> +/*
> + * Creates and starts new thread.
> + *
> + * The thread must be <i>joined</i> with vlc_join() to reclaim resources
> + * when it is not needed anymore.
> + *
> + * @param th [OUT] pointer to write the handle of the created thread to
> + * (mandatory, must be non-NULL)
> + * @param entry entry point for the thread
> + * @param data data parameter given to the entry point
> + * @param priority thread priority value
> + * @return 0 on success, a standard error code on error.
> + */
> +int vlc_clone (vlc_thread_t *th, void *(*entry) (void *), void *data,
> + int priority)
> +{
> + pthread_attr_t attr;
> +
> + pthread_attr_init (&attr);
> + return vlc_clone_attr (th, &attr, entry, data, priority);
> +}
> +
> +/*
> + * Waits for a thread to complete (if needed), then destroys it.
> + * This is a cancellation point; in case of cancellation, the join does
> _not_ + * occur.
> + * @warning
> + * A thread cannot join itself (normally VLC will abort if this is
> attempted). + * Also, a detached thread <b>cannot</b> be joined.
> + *
> + * @param handle thread handle
> + * @param p_result [OUT] pointer to write the thread return value or NULL
> + */
> +void vlc_join (vlc_thread_t handle, void **result)
> +{
> + do {
> + vlc_testcancel();
> + msleep(CLOCK_FREQ / 100);
> + } while (!handle->finished);
Memory access to finished is not thread-safe here. AFAICT, this could lead to
inifinite loops on SMP.
> +
> + int val = pthread_join (handle->thread, result);
> + VLC_THREAD_ASSERT ("joining thread");
> + vlc_mutex_destroy(&handle->lock);
> + free(handle);
> +}
> +
> +/*
> + * Creates and starts new detached thread.
> + * A detached thread cannot be joined. Its resources will be automatically
> + * released whenever the thread exits (in particular, its call stack will
> be + * reclaimed).
> + *
> + * Detached thread are particularly useful when some work needs to be done
> + * asynchronously, that is likely to be completed much earlier than the
> thread + * can practically be joined. In this case, thread detach can
> spare memory. + *
> + * A detached thread may be cancelled, so as to expedite its termination.
> + * Be extremely careful if you do this: while a normal joinable thread can
> + * safely be cancelled after it has already exited, cancelling an already
> + * exited detached thread is undefined: The thread handle would is
> destroyed + * immediately when the detached thread exits. So you need to
> ensure that the + * detached thread is still running before cancellation
> is attempted. + *
> + * @warning Care must be taken that any resources used by the detached
> thread + * remains valid until the thread completes.
> + *
> + * @note A detached thread must eventually exit just like another other
> + * thread. In practice, LibVLC will wait for detached threads to exit
> before + * it unloads the plugins.
> + *
> + * @param th [OUT] pointer to hold the thread handle, or NULL
> + * @param entry entry point for the thread
> + * @param data data parameter given to the entry point
> + * @param priority thread priority value
> + * @return 0 on success, a standard error code on error.
> + */
> +int vlc_clone_detach (vlc_thread_t *th, void *(*entry) (void *), void
> *data, + int priority)
> +{
> + vlc_thread_t dummy;
> + pthread_attr_t attr;
> +
> + if (th == NULL)
> + th = &dummy;
> +
> + pthread_attr_init (&attr);
> + pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
> + return vlc_clone_attr (th, &attr, entry, data, priority);
> +}
> +
> +int vlc_set_priority (vlc_thread_t th, int priority)
> +{
> + (void) th; (void) priority;
> + return VLC_SUCCESS;
> +}
> +
> +/*
> + * Marks a thread as cancelled. Next time the target thread reaches a
> + * cancellation point (while not having disabled cancellation), it will
> + * run its cancellation cleanup handler, the thread variable destructors,
> and + * terminate. vlc_join() must be used afterward regardless of a
> thread being + * cancelled or not.
> + */
> +void vlc_cancel (vlc_thread_t thread_id)
> +{
> + thread_id->killed = true;
This memory access is not thread-safe.
Note that on Windows, killed and killable are only accessed from the cancelled
thread, never from the cancelling thread.
> + if (!thread_id->killable)
> + return;
This optimization shortcut is also not thread-safe.
> +
> + vlc_mutex_lock(&thread_id->lock);
> + vlc_cond_t *cond = thread_id->cond;
> +
> + if (cond)
> + pthread_cond_broadcast(cond);
> + vlc_mutex_unlock(&thread_id->lock);
> +}
> +
> +/*
> + * Save the current cancellation state (enabled or disabled), then disable
> + * cancellation for the calling thread.
> + * This function must be called before entering a piece of code that is
> not + * cancellation-safe, unless it can be proven that the calling thread
> will not + * be cancelled.
> + * @return Previous cancellation state (opaque value for
> vlc_restorecancel()). + */
> +int vlc_savecancel (void)
> +{
> + if (!thread) /* not created by VLC, can't be cancelled */
> + return true;
> +
> + int oldstate = thread->killable;
> + thread->killable = false;
> + return oldstate;
> +}
> +
> +/*
> + * Restore the cancellation state for the calling thread.
> + * @param state previous state as returned by vlc_savecancel().
> + * @return Nothing, always succeeds.
> + */
> +void vlc_restorecancel (int state)
> +{
> + if (!thread) /* not created by VLC, can't be cancelled */
> + return;
> +
> + int val = thread->killable != false;
> + VLC_THREAD_ASSERT("restoring cancellation while not disabled");
> + thread->killable = state;
> +}
> +
> +/*
> + * Issues an explicit deferred cancellation point.
> + * This has no effect if thread cancellation is disabled.
> + * This can be called when there is a rather slow non-sleeping operation.
> + * This is also used to force a cancellation point in a function that
> would + * otherwise "not always" be a one (block_FifoGet() is an example).
> + */
> +void vlc_testcancel (void)
> +{
> + if (!thread) /* not created by VLC, can't be cancelled */
> + return;
> + if (!thread->killable || !thread->killed)
> + return;
> +
> + thread->finished = true;
> + pthread_exit(NULL);
> +}
> +
> +/*
> + * Precision monotonic clock.
> + *
> + * In principles, the clock has a precision of 1 MHz. But the actual
> resolution + * may be much lower, especially when it comes to sleeping
> with mwait() or + * msleep(). Most general-purpose operating systems
> provide a resolution of + * only 100 to 1000 Hz.
> + *
> + * @warning The origin date (time value "zero") is not specified. It is
> + * typically the time the kernel started, but this is platform-dependent.
> + * If you need wall clock time, use gettimeofday() instead.
> + *
> + * @return a timestamp in microseconds.
> + */
Another good reason not to copy comments. This does not match.
> +mtime_t mdate (void)
> +{
> + struct timespec ts;
> +
> + if (unlikely(clock_gettime (CLOCK_REALTIME, &ts) != 0))
> + abort ();
> +
> + return (INT64_C(1000000) * ts.tv_sec) + (ts.tv_nsec / 1000);
> +}
> +
> +#undef mwait
> +/*
> + * Waits until a deadline (possibly later due to OS scheduling).
> + * @param deadline timestamp to wait for (see mdate())
> + */
> +void mwait (mtime_t deadline)
> +{
> + deadline -= mdate ();
> + if (deadline > 0)
> + msleep (deadline);
> +}
> +
> +#undef msleep
> +/*
> + * Waits for an interval of time.
> + * @param delay how long to wait (in microseconds)
> + */
> +void msleep (mtime_t delay)
> +{
> + struct timespec ts = mtime_to_ts (delay);
> +
> + vlc_testcancel();
> + for (;;) {
> + struct timespec t = { 0, 10 * 1000 * 1000 };
> + if (ts.tv_sec <= 0 && t.tv_nsec > ts.tv_nsec)
> + t.tv_nsec = ts.tv_nsec;
> + while (nanosleep (&t, &t) == -1) {
> + vlc_testcancel();
> + vlc_assert (errno == EINTR);
> + }
> +
> + ts.tv_nsec -= 10 * 1000 * 1000;
> + if (ts.tv_nsec < 0) {
> + if (--ts.tv_sec < 0)
> + return;
> + ts.tv_nsec += 1000 * 1000 * 1000;
> + }
> + }
> +}
This is very inefficient. At least, you could do the loop in mwait() instead, to
avoid accumulating drift.
> +
> +/*
> + * Count CPUs.
> + * @return number of available (logical) CPUs.
> + */
> +unsigned vlc_GetCPUCount(void)
> +{
> + return sysconf(_SC_NPROCESSORS_CONF);
> +}
--
Rémi Denis-Courmont
http://www.remlab.net/
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