Implement pthread_mutex_lock_any() and pthread_mutex_timedlock_any().

On newer Linux kernels, futex supports a WAIT_MULTIPLE operation that can be
used to implement new locking functionality that allows a given application
thread to sleep while waiting for one of multiple given locks to become
available.

nptl/Makefile

@@ -68,6 +68,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      pthread_getattr_np \
 		      pthread_mutex_init pthread_mutex_destroy \
 		      pthread_mutex_lock pthread_mutex_trylock \
+		      pthread_mutex_lock_any pthread_mutex_timedlock_any \
 		      pthread_mutex_timedlock pthread_mutex_unlock \
 		      pthread_mutex_cond_lock \
 		      pthread_mutexattr_init pthread_mutexattr_destroy \

nptl/Versions

@@ -274,6 +274,8 @@ libpthread {
     mtx_init; mtx_lock; mtx_timedlock; mtx_trylock; mtx_unlock; mtx_destroy;
     call_once; cnd_broadcast; cnd_destroy; cnd_init; cnd_signal;
     cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
+
+    pthread_mutex_lock_any; pthread_mutex_timedlock_any;
   }
 
   GLIBC_2.30 {

nptl/pthreadP.h

@@ -390,6 +390,11 @@ extern int __pthread_mutex_trylock (pthread_mutex_t *_mutex);
 extern int __pthread_mutex_lock (pthread_mutex_t *__mutex);
 extern int __pthread_mutex_timedlock (pthread_mutex_t *__mutex,
      const struct timespec *__abstime);
+extern int __pthread_mutex_lock_any (pthread_mutex_t *__mutex, int mutexcount,
+				     int *outlocked);
+extern int __pthread_mutex_timedlock_any (pthread_mutex_t *__mutex, int count,
+					  const struct timespec *__abstime,
+					  int *outlocked);
 extern int __pthread_mutex_cond_lock (pthread_mutex_t *__mutex)
      attribute_hidden;
 extern void __pthread_mutex_cond_lock_adjust (pthread_mutex_t *__mutex)

nptl/pthread_mutex_lock_any.c

@@ -0,0 +1,37 @@
+/* Copyright (C) 2002-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/param.h>
+#include <not-cancel.h>
+#include "pthreadP.h"
+#include <atomic.h>
+#include <lowlevellock.h>
+#include <stap-probe.h>
+
+int
+__pthread_mutex_lock_any (pthread_mutex_t *mutexlist, int mutexcount,
+			  int *outlocked)
+{
+  return __pthread_mutex_timedlock_any(mutexlist, mutexcount, NULL, outlocked);
+}
+
+weak_alias (__pthread_mutex_lock_any, pthread_mutex_lock_any)

nptl/pthread_mutex_timedlock_any.c

@@ -0,0 +1,193 @@
+/* Copyright (C) 2002-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/param.h>
+#include <not-cancel.h>
+#include "pthreadP.h"
+#include <atomic.h>
+#include <lowlevellock.h>
+#include <stap-probe.h>
+
+/* TODO: this probably comes from a kernel header when upstream? */
+struct futex_wait_block {
+	int *uaddr;
+	int val;
+	int bitset;
+} __attribute__((packed));
+
+int
+__pthread_mutex_timedlock_any (pthread_mutex_t *mutexlist, int mutexcount,
+			       const struct timespec *abstime, int *outlocked)
+{
+  /* This requires futex support */
+#ifndef __NR_futex
+  return ENOTSUP;
+#endif
+
+  if (mutexlist == NULL)
+  {
+    /* User is asking us if kernel supports the feature. */
+
+    /* TODO: how does one check if supported?
+     * I was thinking of trying the ioctl once and then returning the static
+     * cached value, is that OK?
+     */
+    return 0;
+  }
+
+  if (mutexlist != NULL && mutexcount <= 0)
+    return EINVAL;
+
+  if (outlocked == NULL)
+    return EINVAL;
+
+  int type = PTHREAD_MUTEX_TYPE (mutexlist);
+
+  for (int i = 1; i < mutexcount; i++)
+  {
+    /* Types have to match, since the PRIVATE flag is OP-global. */
+    if (PTHREAD_MUTEX_TYPE (&mutexlist[i]) != type)
+      return EINVAL;
+  }
+
+  int kind = type & PTHREAD_MUTEX_KIND_MASK_NP;
+
+  /* TODO: implement recursive, errorcheck and adaptive. */
+  if (kind != PTHREAD_MUTEX_NORMAL)
+    return EINVAL;
+
+  /* TODO: implement robust. */
+  if (type & PTHREAD_MUTEX_ROBUST_NORMAL_NP)
+    return EINVAL;
+
+  /* TODO: implement PI. */
+  if (type & PTHREAD_MUTEX_PRIO_INHERIT_NP)
+    return EINVAL;
+
+  /* TODO: implement PP. */
+  if (type & PTHREAD_MUTEX_PRIO_PROTECT_NP)
+    return EINVAL;
+
+  pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
+  int result;
+
+  result = -1;
+
+  for (int i = 0; i < mutexcount; i++)
+  {
+    if (__lll_trylock (&mutexlist[i].__data.__lock) == 0)
+    {
+      result = i;
+      break;
+    }
+  }
+
+  while (result == -1)
+  {
+    for (int i = 0; i < mutexcount; i++)
+    {
+      int oldval = atomic_exchange_acq (&mutexlist[i].__data.__lock, 2);
+
+      if (oldval == 0)
+      {
+	result = i;
+	break;
+      }
+    }
+
+    if (result == -1)
+    {
+      /* Couldn't get one of the locks immediately, we have to sleep now. */
+      struct timespec *timeout = NULL;
+      struct timespec rt;
+
+      if (abstime != NULL)
+      {
+	/* Reject invalid timeouts. */
+	if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
+	  return EINVAL;
+
+	struct timeval tv;
+
+	/* Get the current time.  */
+	(void) __gettimeofday (&tv, NULL);
+
+	/* Compute relative timeout.  */
+	rt.tv_sec = abstime->tv_sec - tv.tv_sec;
+	rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
+	if (rt.tv_nsec < 0)
+	{
+	  rt.tv_nsec += 1000000000;
+	  --rt.tv_sec;
+	}
+
+	if (rt.tv_sec < 0)
+	  return ETIMEDOUT;
+
+	timeout = &rt;
+      }
+
+      struct futex_wait_block waitblock[mutexcount];
+
+      for (int i = 0; i < mutexcount; i++)
+      {
+	waitblock[i].uaddr = &mutexlist[i].__data.__lock;
+	waitblock[i].val = 2;
+	waitblock[i].bitset = ~0;
+      }
+
+      long int __ret;
+
+      /* Safe to use the flag for the first one, since all their types match. */
+      int private_flag = PTHREAD_MUTEX_PSHARED (&mutexlist[0]);
+
+      __ret = lll_futex_timed_wait_multiple (waitblock, mutexcount, timeout,
+					    private_flag);
+
+      if (__ret < 0)
+	return -__ret; /* TODO is this correct? */
+
+      /* Have slept, try grabbing the one that woke us up? */
+      if (atomic_exchange_acq (&mutexlist[__ret].__data.__lock, 2) == 0)
+      {
+	/* We got it, done, loop will end below. */
+	result = __ret;
+      }
+    }
+  }
+
+  if (result != -1)
+  {
+    /* Record the ownership. */
+    mutexlist[result].__data.__owner = id;
+    ++mutexlist[result].__data.__nusers;
+
+    /* Let the user know which mutex is now locked. */
+    *outlocked = result;
+
+    result = 0;
+  }
+
+  return result;
+}
+
+weak_alias (__pthread_mutex_timedlock_any, pthread_mutex_timedlock_any)

sysdeps/nptl/pthread.h

@@ -763,7 +763,17 @@ extern int pthread_mutex_trylock (pthread_mutex_t *__mutex)
 extern int pthread_mutex_lock (pthread_mutex_t *__mutex)
      __THROWNL __nonnull ((1));
 
+/* Lock any one of several mutexes.  */
+extern int pthread_mutex_lock_any (pthread_mutex_t *__mutexlist,
+				   int mutexcount, int *outlocked);
+
 #ifdef __USE_XOPEN2K
+/* Lock any one of several mutexes, with timeout.  */
+extern int pthread_mutex_timedlock_any (pthread_mutex_t *__mutexlist,
+					int mutexcount,
+					const struct timespec *__restrict
+					__abstime, int *outlocked);
+
 /* Wait until lock becomes available, or specified time passes. */
 extern int pthread_mutex_timedlock (pthread_mutex_t *__restrict __mutex,
 				    const struct timespec *__restrict

sysdeps/unix/sysv/linux/lowlevellock-futex.h

@@ -38,6 +38,7 @@
 #define FUTEX_WAKE_BITSET	10
 #define FUTEX_WAIT_REQUEUE_PI   11
 #define FUTEX_CMP_REQUEUE_PI    12
+#define FUTEX_WAIT_MULTIPLE     13
 #define FUTEX_PRIVATE_FLAG	128
 #define FUTEX_CLOCK_REALTIME	256
 
@@ -74,6 +75,15 @@
      ? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : 0);                     \
   })
 
+#define lll_futex_syscall_ret(nargs, futexp, op, ...)                   \
+  ({                                                                    \
+    INTERNAL_SYSCALL_DECL (__err);                                      \
+    long int __ret = INTERNAL_SYSCALL (futex, __err, nargs, futexp, op, \
+				       __VA_ARGS__);                    \
+    (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret, __err))         \
+     ? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : __ret);                 \
+  })
+
 #define lll_futex_wait(futexp, val, private) \
   lll_futex_timed_wait (futexp, val, NULL, private)
 
@@ -82,6 +92,11 @@
 		     __lll_private_flag (FUTEX_WAIT, private),  \
 		     val, timeout)
 
+#define lll_futex_timed_wait_multiple(futexp, val, timeout, private)     \
+  lll_futex_syscall_ret (4, futexp,                                      \
+		     __lll_private_flag (FUTEX_WAIT_MULTIPLE, private),  \
+		     val, timeout)
+
 /* Verify whether the supplied clockid is supported by
    lll_futex_clock_wait_bitset.  */
 #define lll_futex_supported_clockid(clockid)			\

sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist

@@ -126,6 +126,7 @@ GLIBC_2.2.5 pthread_kill_other_threads_np F
 GLIBC_2.2.5 pthread_mutex_destroy F
 GLIBC_2.2.5 pthread_mutex_init F
 GLIBC_2.2.5 pthread_mutex_lock F
+GLIBC_2.2.5 pthread_mutex_lock_any F
 GLIBC_2.2.5 pthread_mutex_timedlock F
 GLIBC_2.2.5 pthread_mutex_trylock F
 GLIBC_2.2.5 pthread_mutex_unlock F