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pthreads: Add more robustness characteristics: pthread_mutex_lock() and trylock() will now return EOWNERDEAD if the mutex is locked by a thread that no longer exists. Add pthread_mutex_consistent() to recover from this situation.

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This commit is contained in:
Gregory Nutt
2017-03-26 10:35:23 -06:00
parent bacc4e9b93
commit 363403fb1f
8 changed files with 343 additions and 92 deletions
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sched/pthread/pthread_mutextrylock.c
+60 -30
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@@ -1,7 +1,7 @@
/****************************************************************************
* sched/pthread/pthread_mutextrylock.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@@ -43,6 +43,7 @@
#include <pthread.h>
#include <semaphore.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
@@ -83,15 +84,13 @@
int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
{
int ret = OK;
int status;
int ret = EINVAL;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (!mutex)
{
ret = EINVAL;
}
else
if (mutex != NULL)
{
int mypid = (int)getpid();
@@ -103,7 +102,8 @@ int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
/* Try to get the semaphore. */
if (sem_trywait((FAR sem_t *)&mutex->sem) == OK)
status = sem_trywait((FAR sem_t *)&mutex->sem);
if (status == OK)
{
/* If we successfully obtained the semaphore, then indicate
* that we own it.
@@ -117,33 +117,63 @@ int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
mutex->nlocks = 1;
}
#endif
ret = OK;
}
/* Was it not available? */
/* sem_trywait failed */
else if (get_errno() == EAGAIN)
{
#ifdef CONFIG_MUTEX_TYPES
/* Check if recursive mutex was locked by ourself. */
if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->pid == mypid)
{
/* Increment the number of locks held and return successfully. */
mutex->nlocks++;
}
else
{
ret = EBUSY;
}
#else
ret = EBUSY;
#endif
}
else
{
ret = EINVAL;
/* Did it fail because the semaphore was not avaialabl? */
int errcode = get_errno();
if (errcode == EAGAIN)
{
#ifdef CONFIG_MUTEX_TYPES
/* Check if recursive mutex was locked by the calling thread. */
if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->pid == mypid)
{
/* Increment the number of locks held and return successfully. */
mutex->nlocks++;
ret = OK;
}
else
#endif
/* The calling thread does not hold the semaphore. The correct
* behavior for the 'robust' mutex is to verify that the holder of
* the mutex is still valid. This is protection from the case
* where the holder of the mutex has exitted without unlocking it.
*/
if (mutex->pid > 0 && sched_gettcb(mutex->pid) == NULL)
{
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
/* A thread holds the mutex, but there is no such thread.
* POSIX requires that the 'robust' mutex return EOWNERDEAD
* in this case. It is then the caller's responsibility to
* call pthread_mutx_consistent() fo fix the mutex.
*/
ret = EOWNERDEAD;
}
/* The mutex is locked by another, active thread */
else
{
ret = EBUSY;
}
}
/* Some other, unhandled error occurred */
else
{
ret = errcode;
}
}
sched_unlock();