/* $OpenBSD: uthread_file.c,v 1.10 2003/01/31 04:46:17 marc Exp $ */ /* * Copyright (c) 1995 John Birrell . * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by John Birrell. * 4. Neither the name of the author nor the names of any co-contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * $FreeBSD: uthread_file.c,v 1.9 1999/08/28 00:03:32 peter Exp $ * * POSIX stdio FILE locking functions. These assume that the locking * is only required at FILE structure level, not at file descriptor * level too. * */ #include #include #include #include #ifdef _THREAD_SAFE #include #include "pthread_private.h" /* * The FILE lock structure. The FILE *fp is locked if the owner is * not NULL. If not locked, the file lock structure can be * reassigned to a different file by setting fp. */ struct file_lock { LIST_ENTRY(file_lock) entry; /* Entry if file list. */ V_TAILQ_HEAD(lock_head, pthread) l_head; /* Head of queue for threads */ /* waiting on this lock. */ FILE *fp; /* The target file. */ pthread_t owner; /* Thread that owns lock. */ int count; /* Lock count for owner. */ }; /* * The number of file lock lists into which the file pointer is * hashed. Ideally, the FILE structure size would have been increased, * but this causes incompatibility, so separate data structures are * required. */ #define NUM_HEADS 128 /* * This macro casts a file pointer to a long integer and right * shifts this by the number of bytes in a pointer. The shifted * value is then remaindered using the maximum number of hash * entries to produce and index into the array of static lock * structures. If there is a collision, a linear search of the * dynamic list of locks linked to each static lock is perfomed. */ #define file_idx(_p) ((((u_long) _p) >> sizeof(void *)) % NUM_HEADS) /* * Global array of file locks. The first lock for each hash bucket is * allocated statically in the hope that there won't be too many * collisions that require a malloc and an element added to the list. */ struct static_file_lock { LIST_HEAD(file_list_head, file_lock) head; struct file_lock fl; } flh[NUM_HEADS]; /* Set to non-zero when initialisation is complete: */ static int init_done = 0; /* Lock for accesses to the hash table: */ static spinlock_t hash_lock = _SPINLOCK_INITIALIZER; /* * Find a lock structure for a FILE, return NULL if the file is * not locked: */ static struct file_lock * find_lock(int idx, FILE *fp) { struct file_lock *p; /* Check if the file is locked using the static structure: */ if (flh[idx].fl.fp == fp && flh[idx].fl.owner != NULL) /* Return a pointer to the static lock: */ p = &flh[idx].fl; else { /* Point to the first dynamic lock: */ p = flh[idx].head.lh_first; /* * Loop through the dynamic locks looking for the * target file: */ while (p != NULL && (p->fp != fp || p->owner == NULL)) /* Not this file, try the next: */ p = p->entry.le_next; } return(p); } /* * Lock a file, assuming that there is no lock structure currently * assigned to it. */ static struct file_lock * do_lock(int idx, FILE *fp) { struct file_lock *p; /* Check if the static structure is not being used: */ if (flh[idx].fl.owner == NULL) { /* Return a pointer to the static lock: */ p = &flh[idx].fl; } else { /* Point to the first dynamic lock: */ p = flh[idx].head.lh_first; /* * Loop through the dynamic locks looking for a * lock structure that is not being used: */ while (p != NULL && p->owner != NULL) /* This one is used, try the next: */ p = p->entry.le_next; } /* * If an existing lock structure has not been found, * allocate memory for a new one: */ if (p == NULL && (p = (struct file_lock *) malloc(sizeof(struct file_lock))) != NULL) { /* Add the new element to the list: */ LIST_INSERT_HEAD(&flh[idx].head, p, entry); } /* Check if there is a lock structure to acquire: */ if (p != NULL) { /* Acquire the lock for the running thread: */ p->fp = fp; p->owner = _thread_run; p->count = 1; TAILQ_INIT(&p->l_head); } return(p); } void _flockfile_debug(FILE * fp, char *fname, int lineno) { int idx = file_idx(fp); struct file_lock *p; /* Check if this is a real file: */ if (fp->_file >= 0) { /* Lock the hash table: */ _SPINLOCK(&hash_lock); /* Check if the static array has not been initialised: */ if (!init_done) { /* Initialise the global array: */ memset(flh,0,sizeof(flh)); /* Flag the initialisation as complete: */ init_done = 1; } /* Get a pointer to any existing lock for the file: */ if ((p = find_lock(idx, fp)) == NULL) { /* * The file is not locked, so this thread can * grab the lock: */ p = do_lock(idx, fp); /* Unlock the hash table: */ _SPINUNLOCK(&hash_lock); /* * The file is already locked, so check if the * running thread is the owner: */ } else if (p->owner == _thread_run) { /* * The running thread is already the * owner, so increment the count of * the number of times it has locked * the file: */ p->count++; /* Unlock the hash table: */ _SPINUNLOCK(&hash_lock); } else { /* * The file is locked for another thread. * Append this thread to the queue of * threads waiting on the lock. */ TAILQ_INSERT_TAIL(&p->l_head,_thread_run,qe); /* Unlock the hash table: */ _SPINUNLOCK(&hash_lock); /* Wait on the FILE lock: */ _thread_kern_sched_state(PS_FILE_WAIT, fname, lineno); } } return; } void flockfile(FILE * fp) { _flockfile_debug(fp, (char *) "?", 1); return; } int ftrylockfile(FILE * fp) { int ret = -1; int idx = file_idx(fp); struct file_lock *p; /* Check if this is a real file: */ if (fp->_file >= 0) { /* Lock the hash table: */ _SPINLOCK(&hash_lock); /* Get a pointer to any existing lock for the file: */ if ((p = find_lock(idx, fp)) == NULL) { /* * The file is not locked, so this thread can * grab the lock: */ p = do_lock(idx, fp); /* * The file is already locked, so check if the * running thread is the owner: */ } else if (p->owner == _thread_run) { /* * The running thread is already the * owner, so increment the count of * the number of times it has locked * the file: */ p->count++; } else { /* * The file is locked for another thread, * so this try fails. */ p = NULL; } /* Check if the lock was obtained: */ if (p != NULL) /* Return success: */ ret = 0; /* Unlock the hash table: */ _SPINUNLOCK(&hash_lock); } return (ret); } void funlockfile(FILE * fp) { int idx = file_idx(fp); struct file_lock *p; /* Check if this is a real file: */ if (fp->_file >= 0) { /* * Defer signals to protect the scheduling queues from * access by the signal handler: */ _thread_kern_sig_defer(); /* Lock the hash table: */ _SPINLOCK(&hash_lock); /* * Get a pointer to the lock for the file and check that * the running thread is the one with the lock: */ if ((p = find_lock(idx, fp)) != NULL && p->owner == _thread_run) { /* * Check if this thread has locked the FILE * more than once: */ if (p->count > 1) /* * Decrement the count of the number of * times the running thread has locked this * file: */ p->count--; else { /* * The running thread will release the * lock now: */ p->count = 0; /* Get the new owner of the lock: */ if ((p->owner = TAILQ_FIRST(&p->l_head)) != NULL) { /* Pop the thread off the queue: */ TAILQ_REMOVE(&p->l_head,p->owner,qe); /* * This is the first lock for the new * owner: */ p->count = 1; /* Allow the new owner to run: */ PTHREAD_NEW_STATE(p->owner,PS_RUNNING); } } } /* Unlock the hash table: */ _SPINUNLOCK(&hash_lock); /* * Undefer and handle pending signals, yielding if * necessary: */ _thread_kern_sig_undefer(); } return; } #endif