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