(PHP 4 >= 4.2.0, PHP 5 < 5.1.0) dio_open — Opens a file (creating it if necessary) at a lower level than the C library input/ouput stream functions allow dio_open(string $filename, int $flags, int $mode = 0): resource The pathname of the file to open.
The flags parameter is a bitwise-ORed value comprising flags from the following list. This value must include one of O_RDONLY, O_WRONLY, or O_RDWR. Additionally, it may include any combination of the other flags from this list. O_RDONLY - opens the file for read access. O_WRONLY - opens the file for write access. O_RDWR -
opens the file for both reading and writing. O_CREAT - creates the file, if it doesn't already exist. O_EXCL - if both O_CREAT and O_EXCL are set and the file already exists, dio_open() will fail. O_TRUNC - if the file exists and is opened for write access, the file will be truncated to zero length. 说明
参数
filename
O_APPEND - write operations write data at the end of the file.
O_NONBLOCK - sets non blocking mode.
O_NOCTTY - prevent the OS from assigning the opened file as the process's controlling terminal when opening a TTY device file.
If flags contains O_CREAT, mode will set the permissions of the file (creation permissions). mode is required for correct operation when O_CREAT is specified in flags and is ignored otherwise.
The actual permissions assigned to the created file will be affected by the process's umask setting as per usual.
返回值
A file descriptor or false on error.
范例
示例 #1 Opening a file descriptor
<?php
$fd
= dio_open('/dev/ttyS0', O_RDWR | O_NOCTTY | O_NONBLOCK);dio_close($fd);?>
参见
- dio_close() - Closes the file descriptor given by fd
Marius Karthaus ¶
12 years ago
One of the prominent reasons to use direct IO, is for it's ability to do actual direct IO, bypassing the operating system cache and getting the data from the disk directly.
The flag to do that (O_DIRECT) is missing from the documentation above. Maybe for good reasons, because this type of IO only works on blockdevices, not on files, and should only be used if you are **really** sure what you are doing.
j at pureftpd dot org ¶
17 years ago
Please note that dio_open()/dio_write()/dio_close() is *faster* than fopen()/fwrite()/fclose() for files.
fwrite() has to manage a 8k buffer, while dio_write() just issue a single write(). The end result is less system calls and less memory access.
Also, giving the full size to write() as with dio_write() let filesystems properly use preallocation in order to avoid fragmentation.
Anonymous ¶
10 years ago
"The prominent reason" to use direct I/O is when your application provides its own cache feature, so you won't do double caching
alla at cyber dot com dot au ¶
19 years ago
To specify a combination of flags you OR them together.
This was the only way I could get it to append:
$fd = dio_open($file, O_WRONLY | O_APPEND);
Here is the code that generates the id: Session.c
Specifically the php_session_create_id function:
PHPAPI char *php_session_create_id(PS_CREATE_SID_ARGS) /* {{{ */ { PHP_MD5_CTX md5_context; PHP_SHA1_CTX sha1_context; #if defined(HAVE_HASH_EXT) && !defined(COMPILE_DL_HASH) void *hash_context = NULL; #endif unsigned char *digest; int digest_len; int j; char *buf, *outid; struct timeval tv; zval **array; zval **token; char *remote_addr = NULL; gettimeofday(&tv, NULL); if (zend_hash_find(&EG(symbol_table), "_SERVER", sizeof("_SERVER"), (void **) &array) == SUCCESS && Z_TYPE_PP(array) == IS_ARRAY && zend_hash_find(Z_ARRVAL_PP(array), "REMOTE_ADDR", sizeof("REMOTE_ADDR"), (void **) &token) == SUCCESS ) { remote_addr = Z_STRVAL_PP(token); } /* maximum 15+19+19+10 bytes */ spprintf(&buf, 0, "%.15s%ld%ld%0.8F", remote_addr ? remote_addr : "", tv.tv_sec, (long int)tv.tv_usec, php_combined_lcg(TSRMLS_C) * 10); switch (PS(hash_func)) { case PS_HASH_FUNC_MD5: PHP_MD5Init(&md5_context); PHP_MD5Update(&md5_context, (unsigned char *) buf, strlen(buf)); digest_len = 16; break; case PS_HASH_FUNC_SHA1: PHP_SHA1Init(&sha1_context); PHP_SHA1Update(&sha1_context, (unsigned char *) buf, strlen(buf)); digest_len = 20; break; #if defined(HAVE_HASH_EXT) && !defined(COMPILE_DL_HASH) case PS_HASH_FUNC_OTHER: if (!PS(hash_ops)) { php_error_docref(NULL TSRMLS_CC, E_ERROR, "Invalid session hash function"); efree(buf); return NULL; } hash_context = emalloc(PS(hash_ops)->context_size); PS(hash_ops)->hash_init(hash_context); PS(hash_ops)->hash_update(hash_context, (unsigned char *) buf, strlen(buf)); digest_len = PS(hash_ops)->digest_size; break; #endif /* HAVE_HASH_EXT */ default: php_error_docref(NULL TSRMLS_CC, E_ERROR, "Invalid session hash function"); efree(buf); return NULL; } efree(buf); if (PS(entropy_length) > 0) { #ifdef PHP_WIN32 unsigned char rbuf[2048]; size_t toread = PS(entropy_length); if (php_win32_get_random_bytes(rbuf, MIN(toread, sizeof(rbuf))) == SUCCESS){ switch (PS(hash_func)) { case PS_HASH_FUNC_MD5: PHP_MD5Update(&md5_context, rbuf, toread); break; case PS_HASH_FUNC_SHA1: PHP_SHA1Update(&sha1_context, rbuf, toread); break; # if defined(HAVE_HASH_EXT) && !defined(COMPILE_DL_HASH) case PS_HASH_FUNC_OTHER: PS(hash_ops)->hash_update(hash_context, rbuf, toread); break; # endif /* HAVE_HASH_EXT */ } } #else int fd; fd = VCWD_OPEN(PS(entropy_file), O_RDONLY); if (fd >= 0) { unsigned char rbuf[2048]; int n; int to_read = PS(entropy_length); while (to_read > 0) { n = read(fd, rbuf, MIN(to_read, sizeof(rbuf))); if (n <= 0) break; switch (PS(hash_func)) { case PS_HASH_FUNC_MD5: PHP_MD5Update(&md5_context, rbuf, n); break; case PS_HASH_FUNC_SHA1: PHP_SHA1Update(&sha1_context, rbuf, n); break; #if defined(HAVE_HASH_EXT) && !defined(COMPILE_DL_HASH) case PS_HASH_FUNC_OTHER: PS(hash_ops)->hash_update(hash_context, rbuf, n); break; #endif /* HAVE_HASH_EXT */ } to_read -= n; } close(fd); } #endif } digest = emalloc(digest_len + 1); switch (PS(hash_func)) { case PS_HASH_FUNC_MD5: PHP_MD5Final(digest, &md5_context); break; case PS_HASH_FUNC_SHA1: PHP_SHA1Final(digest, &sha1_context); break; #if defined(HAVE_HASH_EXT) && !defined(COMPILE_DL_HASH) case PS_HASH_FUNC_OTHER: PS(hash_ops)->hash_final(digest, hash_context); efree(hash_context); break; #endif /* HAVE_HASH_EXT */ } if (PS(hash_bits_per_character) < 4 || PS(hash_bits_per_character) > 6) { PS(hash_bits_per_character) = 4; php_error_docref(NULL TSRMLS_CC, E_WARNING, "The ini setting hash_bits_per_character is out of range (should be 4, 5, or 6) - using 4 for now"); } outid = emalloc((size_t)((digest_len + 2) * ((8.0f / PS(hash_bits_per_character)) + 0.5))); j = (int) (bin_to_readable((char *)digest, digest_len, outid, (char)PS(hash_bits_per_character)) - outid); efree(digest); if (newlen) { *newlen = j; } return outid; }As you can see the actual id is a hash of a mixture of things, like the time of day. So there is a possibility of running into a conflict, however, it has a very low possibility. So much so, it is not worth worrying about unless you have lots of concurrent users.
However, if you really are worried you can increase the entropy by setting a different hash algorithm session.hash_function
As far as monitoring active sessions, this question covers it well Is it possible to see active sessions using php?
If you are using a single instance of php on a single machine, then it actually has a built in session manager that checks whether an id already exists before assigning it. However, if you are running multiple instances or multiple machines it has no way of knowing what ids have been assigned by other machines.
How is PHP session ID created?
Session ID is created according to php. ini settings. It is important to use the same user ID of your web server for GC task script. Otherwise, you may have permission problems especially with files save handler.
How is session ID generated?
The SessionID value is randomly generated by ASP.NET and stored in a non-expiring session cookie in the browser. The SessionID value is then sent in a cookie with each request to the ASP.NET application.
How can I get PHP session ID in PHP?
Before getting a session id you need to start a session and that is done by using: session_start() function. Now that you have started a session you can get a session id by using: session_id().
Is PHP session ID unique?
The server generates a unique random number, which is called a session id. It also creates a new file on the server which is used to store the session-specific information.