The Tor Browser: nsprpub/pr/src/io/prfdcach.c@6474c204b198 (annotated)

nsprpub/pr/src/io/prfdcach.c@6474c204b198 (annotated)

nsprpub/pr/src/io/prfdcach.c

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- 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;
     PRStack *stack;
     PRFileDesc *head, *tail;
     PRIntn limit_low, limit_high;
 } _PR_Fd_Cache;
 static _PR_Fd_Cache _pr_fd_cache;
 static PRFileDesc **stack2fd = &(((PRFileDesc*)NULL)->higher);
 /*
 ** 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)
     {
         PRStackElem *pop;
         PR_ASSERT(NULL != _pr_fd_cache.stack);
         pop = PR_StackPop(_pr_fd_cache.stack);
         if (NULL == pop) goto allocate;
         fd = (PRFileDesc*)((PRPtrdiff)pop - (PRPtrdiff)stack2fd);
     }
     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)
     {
         PR_StackPush(_pr_fd_cache.stack, (PRStackElem*)(&fd->higher));
     }
     else
     {
         if (_pr_fd_cache.count > _pr_fd_cache.limit_high)
         {
             PR_Free(fd->secret);
             PR_Free(fd);
         }
         else
         {
             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);
         }
     }
 }  /* _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);
     if (0 == high)  /* shutting down or staying down */
     {
         if (0 != _pr_fd_cache.limit_high)  /* shutting down */
         {
             _pr_fd_cache.limit_high = 0;  /* stop use */
             /*
             ** Hold the lock throughout - nobody's going to want it
             ** other than another caller to this routine. Just don't
             ** let that happen.
             **
             ** Put all the cached fds onto the new cache.
             */
             while (NULL != _pr_fd_cache.head)
             {
                 PRFileDesc *fd = _pr_fd_cache.head;
                 _pr_fd_cache.head = fd->higher;
                 PR_StackPush(_pr_fd_cache.stack, (PRStackElem*)(&fd->higher));
             }
             _pr_fd_cache.limit_low = 0;
             _pr_fd_cache.tail = NULL;
             _pr_fd_cache.count = 0;
         }
     }
     else  /* starting up or just adjusting parameters */
     {
         PRBool was_using_stack = (0 == _pr_fd_cache.limit_high);
         _pr_fd_cache.limit_low = low;
         _pr_fd_cache.limit_high = high;
         if (was_using_stack)  /* was using stack - feed into cache */
         {
             PRStackElem *pop;
             while (NULL != (pop = PR_StackPop(_pr_fd_cache.stack)))
             {
                 PRFileDesc *fd = (PRFileDesc*)
                     ((PRPtrdiff)pop - (PRPtrdiff)stack2fd);
                 if (NULL == _pr_fd_cache.tail) _pr_fd_cache.tail = fd;
                 fd->higher = _pr_fd_cache.head;
                 _pr_fd_cache.head = fd;
                 _pr_fd_cache.count += 1;
             }
         }
     }
     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_fd_cache.stack = PR_CreateStack("FD");
     PR_ASSERT(NULL != _pr_fd_cache.stack);
 }  /* _PR_InitFdCache */
 void _PR_CleanupFdCache(void)
 {
     PRFileDesc *fd, *next;
     PRStackElem *pop;
     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;
     while ((pop = PR_StackPop(_pr_fd_cache.stack)) != NULL)
     {
         fd = (PRFileDesc*)((PRPtrdiff)pop - (PRPtrdiff)stack2fd);
         PR_DELETE(fd->secret);
         PR_DELETE(fd);
     }
     PR_DestroyStack(_pr_fd_cache.stack);
     _pr_fd_cache.stack = NULL;
 }  /* _PR_CleanupFdCache */
 /* prfdcach.c */

The Tor Browser / annotate

nsprpub/pr/src/io/prfdcach.c@6474c204b198 (annotated)

nsprpub/pr/src/io/prfdcach.c