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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "primpl.h"
#include <string.h>
/*****************************************************************************/
/*****************************************************************************/
/************************** File descriptor caching **************************/
/*****************************************************************************/
/*****************************************************************************/
/*
** This code is built into debuggable versions of NSPR to assist in
** finding misused file descriptors. Since file descritors (PRFileDesc)
** are identified by a pointer to their structure, they can be the
** target of dangling references. Furthermore, NSPR caches and tries
** to aggressively reuse file descriptors, leading to more ambiguity.
** The following code will allow a debugging client to set environment
** variables and control the number of file descriptors that will be
** preserved before they are recycled. The environment variables are
** NSPR_FD_CACHE_SIZE_LOW and NSPR_FD_CACHE_SIZE_HIGH. The former sets
** the number of descriptors NSPR will allocate before beginning to
** recycle. The latter is the maximum number permitted in the cache
** (exclusive of those in use) at a time.
*/
typedef struct _PR_Fd_Cache
{
PRLock *ml;
PRIntn count;
PRFileDesc *head, *tail;
PRIntn limit_low, limit_high;
} _PR_Fd_Cache;
static _PR_Fd_Cache _pr_fd_cache;
/*
** Get a FileDescriptor from the cache if one exists. If not allocate
** a new one from the heap.
*/
PRFileDesc *_PR_Getfd(void)
{
PRFileDesc *fd;
/*
** $$$
** This may look a little wasteful. We'll see. Right now I want to
** be able to toggle between caching and not at runtime to measure
** the differences. If it isn't too annoying, I'll leave it in.
** $$$$
**
** The test is against _pr_fd_cache.limit_high. If that's zero,
** we're not doing the extended cache but going for performance.
*/
if (0 == _pr_fd_cache.limit_high)
{
goto allocate;
}
else
{
do
{
if (NULL == _pr_fd_cache.head) goto allocate; /* nothing there */
if (_pr_fd_cache.count < _pr_fd_cache.limit_low) goto allocate;
/* we "should" be able to extract an fd from the cache */
PR_Lock(_pr_fd_cache.ml); /* need the lock to do this safely */
fd = _pr_fd_cache.head; /* protected extraction */
if (NULL == fd) /* unexpected, but not fatal */
{
PR_ASSERT(0 == _pr_fd_cache.count);
PR_ASSERT(NULL == _pr_fd_cache.tail);
}
else
{
_pr_fd_cache.count -= 1;
_pr_fd_cache.head = fd->higher;
if (NULL == _pr_fd_cache.head)
{
PR_ASSERT(0 == _pr_fd_cache.count);
_pr_fd_cache.tail = NULL;
}
PR_ASSERT(&_pr_faulty_methods == fd->methods);
PR_ASSERT(PR_INVALID_IO_LAYER == fd->identity);
PR_ASSERT(_PR_FILEDESC_FREED == fd->secret->state);
}
PR_Unlock(_pr_fd_cache.ml);
} while (NULL == fd); /* then go around and allocate a new one */
}
finished:
fd->dtor = NULL;
fd->lower = fd->higher = NULL;
fd->identity = PR_NSPR_IO_LAYER;
memset(fd->secret, 0, sizeof(PRFilePrivate));
return fd;
allocate:
fd = PR_NEW(PRFileDesc);
if (NULL != fd)
{
fd->secret = PR_NEW(PRFilePrivate);
if (NULL == fd->secret) PR_DELETE(fd);
}
if (NULL != fd) goto finished;
else return NULL;
} /* _PR_Getfd */
/*
** Return a file descriptor to the cache unless there are too many in
** there already. If put in cache, clear the fields first.
*/
void _PR_Putfd(PRFileDesc *fd)
{
PR_ASSERT(PR_NSPR_IO_LAYER == fd->identity);
fd->methods = &_pr_faulty_methods;
fd->identity = PR_INVALID_IO_LAYER;
fd->secret->state = _PR_FILEDESC_FREED;
if (0 != _pr_fd_cache.limit_high)
{
if (_pr_fd_cache.count < _pr_fd_cache.limit_high)
{
PR_Lock(_pr_fd_cache.ml);
if (NULL == _pr_fd_cache.tail)
{
PR_ASSERT(0 == _pr_fd_cache.count);
PR_ASSERT(NULL == _pr_fd_cache.head);
_pr_fd_cache.head = _pr_fd_cache.tail = fd;
}
else
{
PR_ASSERT(NULL == _pr_fd_cache.tail->higher);
_pr_fd_cache.tail->higher = fd;
_pr_fd_cache.tail = fd; /* new value */
}
fd->higher = NULL; /* always so */
_pr_fd_cache.count += 1; /* count the new entry */
PR_Unlock(_pr_fd_cache.ml);
return;
}
}
PR_Free(fd->secret);
PR_Free(fd);
} /* _PR_Putfd */
PR_IMPLEMENT(PRStatus) PR_SetFDCacheSize(PRIntn low, PRIntn high)
{
/*
** This can be called at any time, may adjust the cache sizes,
** turn the caches off, or turn them on. It is not dependent
** on the compilation setting of DEBUG.
*/
if (!_pr_initialized) _PR_ImplicitInitialization();
if (low > high) low = high; /* sanity check the params */
PR_Lock(_pr_fd_cache.ml);
_pr_fd_cache.limit_high = high;
_pr_fd_cache.limit_low = low;
PR_Unlock(_pr_fd_cache.ml);
return PR_SUCCESS;
} /* PR_SetFDCacheSize */
void _PR_InitFdCache(void)
{
/*
** The fd caching is enabled by default for DEBUG builds,
** disabled by default for OPT builds. That default can
** be overridden at runtime using environment variables
** or a super-wiz-bang API.
*/
const char *low = PR_GetEnv("NSPR_FD_CACHE_SIZE_LOW");
const char *high = PR_GetEnv("NSPR_FD_CACHE_SIZE_HIGH");
/*
** _low is allowed to be zero, _high is not.
** If _high is zero, we're not doing the caching.
*/
_pr_fd_cache.limit_low = 0;
#if defined(DEBUG)
_pr_fd_cache.limit_high = FD_SETSIZE;
#else
_pr_fd_cache.limit_high = 0;
#endif /* defined(DEBUG) */
if (NULL != low) _pr_fd_cache.limit_low = atoi(low);
if (NULL != high) _pr_fd_cache.limit_high = atoi(high);
if (_pr_fd_cache.limit_low < 0)
_pr_fd_cache.limit_low = 0;
if (_pr_fd_cache.limit_low > FD_SETSIZE)
_pr_fd_cache.limit_low = FD_SETSIZE;
if (_pr_fd_cache.limit_high > FD_SETSIZE)
_pr_fd_cache.limit_high = FD_SETSIZE;
if (_pr_fd_cache.limit_high < _pr_fd_cache.limit_low)
_pr_fd_cache.limit_high = _pr_fd_cache.limit_low;
_pr_fd_cache.ml = PR_NewLock();
PR_ASSERT(NULL != _pr_fd_cache.ml);
} /* _PR_InitFdCache */
void _PR_CleanupFdCache(void)
{
PRFileDesc *fd, *next;
for (fd = _pr_fd_cache.head; fd != NULL; fd = next)
{
next = fd->higher;
PR_DELETE(fd->secret);
PR_DELETE(fd);
}
_pr_fd_cache.head = NULL;
_pr_fd_cache.tail = NULL;
_pr_fd_cache.count = 0;
PR_DestroyLock(_pr_fd_cache.ml);
_pr_fd_cache.ml = NULL;
} /* _PR_CleanupFdCache */
/* prfdcach.c */
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