/* -*- 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 */