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diff --git a/gcc-4.8.1/libstdc++-v3/doc/html/manual/mt_allocator_impl.html b/gcc-4.8.1/libstdc++-v3/doc/html/manual/mt_allocator_impl.html deleted file mode 100644 index a93f2a0dd..000000000 --- a/gcc-4.8.1/libstdc++-v3/doc/html/manual/mt_allocator_impl.html +++ /dev/null @@ -1,160 +0,0 @@ -<?xml version="1.0" encoding="UTF-8" standalone="no"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Implementation</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, allocator" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="mt_allocator.html" title="Chapter 20. The mt_allocator" /><link rel="prev" href="mt_allocator_design.html" title="Design Issues" /><link rel="next" href="mt_allocator_ex_single.html" title="Single Thread Example" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Implementation</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="mt_allocator_design.html">Prev</a> </td><th width="60%" align="center">Chapter 20. The mt_allocator</th><td width="20%" align="right"> <a accesskey="n" href="mt_allocator_ex_single.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="allocator.mt.impl"></a>Implementation</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="allocator.mt.tune"></a>Tunable Parameters</h3></div></div></div><p>Certain allocation parameters can be modified, or tuned. There -exists a nested <code class="code">struct __pool_base::_Tune</code> that contains all -these parameters, which include settings for -</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Alignment</p></li><li class="listitem"><p>Maximum bytes before calling <code class="code">::operator new</code> directly</p></li><li class="listitem"><p>Minimum bytes</p></li><li class="listitem"><p>Size of underlying global allocations</p></li><li class="listitem"><p>Maximum number of supported threads</p></li><li class="listitem"><p>Migration of deallocations to the global free list</p></li><li class="listitem"><p>Shunt for global <code class="code">new</code> and <code class="code">delete</code></p></li></ul></div><p>Adjusting parameters for a given instance of an allocator can only -happen before any allocations take place, when the allocator itself is -initialized. For instance: -</p><pre class="programlisting"> -#include <ext/mt_allocator.h> - -struct pod -{ - int i; - int j; -}; - -int main() -{ - typedef pod value_type; - typedef __gnu_cxx::__mt_alloc<value_type> allocator_type; - typedef __gnu_cxx::__pool_base::_Tune tune_type; - - tune_type t_default; - tune_type t_opt(16, 5120, 32, 5120, 20, 10, false); - tune_type t_single(16, 5120, 32, 5120, 1, 10, false); - - tune_type t; - t = allocator_type::_M_get_options(); - allocator_type::_M_set_options(t_opt); - t = allocator_type::_M_get_options(); - - allocator_type a; - allocator_type::pointer p1 = a.allocate(128); - allocator_type::pointer p2 = a.allocate(5128); - - a.deallocate(p1, 128); - a.deallocate(p2, 5128); - - return 0; -} -</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="allocator.mt.init"></a>Initialization</h3></div></div></div><p> -The static variables (pointers to freelists, tuning parameters etc) -are initialized as above, or are set to the global defaults. -</p><p> -The very first allocate() call will always call the -_S_initialize_once() function. In order to make sure that this -function is called exactly once we make use of a __gthread_once call -in MT applications and check a static bool (_S_init) in ST -applications. -</p><p> -The _S_initialize() function: -- If the GLIBCXX_FORCE_NEW environment variable is set, it sets the bool - _S_force_new to true and then returns. This will cause subsequent calls to - allocate() to return memory directly from a new() call, and deallocate will - only do a delete() call. -</p><p> -- If the GLIBCXX_FORCE_NEW environment variable is not set, both ST and MT - applications will: - - Calculate the number of bins needed. A bin is a specific power of two size - of bytes. I.e., by default the allocator will deal with requests of up to - 128 bytes (or whatever the value of _S_max_bytes is when _S_init() is - called). This means that there will be bins of the following sizes - (in bytes): 1, 2, 4, 8, 16, 32, 64, 128. - - - Create the _S_binmap array. All requests are rounded up to the next - "large enough" bin. I.e., a request for 29 bytes will cause a block from - the "32 byte bin" to be returned to the application. The purpose of - _S_binmap is to speed up the process of finding out which bin to use. - I.e., the value of _S_binmap[ 29 ] is initialized to 5 (bin 5 = 32 bytes). -</p><p> - - Create the _S_bin array. This array consists of bin_records. There will be - as many bin_records in this array as the number of bins that we calculated - earlier. I.e., if _S_max_bytes = 128 there will be 8 entries. - Each bin_record is then initialized: - - bin_record->first = An array of pointers to block_records. There will be - as many block_records pointers as there are maximum number of threads - (in a ST application there is only 1 thread, in a MT application there - are _S_max_threads). - This holds the pointer to the first free block for each thread in this - bin. I.e., if we would like to know where the first free block of size 32 - for thread number 3 is we would look this up by: _S_bin[ 5 ].first[ 3 ] - - The above created block_record pointers members are now initialized to - their initial values. I.e. _S_bin[ n ].first[ n ] = NULL; -</p><p> -- Additionally a MT application will: - - Create a list of free thread id's. The pointer to the first entry - is stored in _S_thread_freelist_first. The reason for this approach is - that the __gthread_self() call will not return a value that corresponds to - the maximum number of threads allowed but rather a process id number or - something else. So what we do is that we create a list of thread_records. - This list is _S_max_threads long and each entry holds a size_t thread_id - which is initialized to 1, 2, 3, 4, 5 and so on up to _S_max_threads. - Each time a thread calls allocate() or deallocate() we call - _S_get_thread_id() which looks at the value of _S_thread_key which is a - thread local storage pointer. If this is NULL we know that this is a newly - created thread and we pop the first entry from this list and saves the - pointer to this record in the _S_thread_key variable. The next time - we will get the pointer to the thread_record back and we use the - thread_record->thread_id as identification. I.e., the first thread that - calls allocate will get the first record in this list and thus be thread - number 1 and will then find the pointer to its first free 32 byte block - in _S_bin[ 5 ].first[ 1 ] - When we create the _S_thread_key we also define a destructor - (_S_thread_key_destr) which means that when the thread dies, this - thread_record is returned to the front of this list and the thread id - can then be reused if a new thread is created. - This list is protected by a mutex (_S_thread_freelist_mutex) which is only - locked when records are removed or added to the list. -</p><p> - - Initialize the free and used counters of each bin_record: - - bin_record->free = An array of size_t. This keeps track of the number - of blocks on a specific thread's freelist in each bin. I.e., if a thread - has 12 32-byte blocks on it's freelists and allocates one of these, this - counter would be decreased to 11. - - - bin_record->used = An array of size_t. This keeps track of the number - of blocks currently in use of this size by this thread. I.e., if a thread - has made 678 requests (and no deallocations...) of 32-byte blocks this - counter will read 678. - - The above created arrays are now initialized with their initial values. - I.e. _S_bin[ n ].free[ n ] = 0; -</p><p> - - Initialize the mutex of each bin_record: The bin_record->mutex - is used to protect the global freelist. This concept of a global - freelist is explained in more detail in the section "A multi - threaded example", but basically this mutex is locked whenever a - block of memory is retrieved or returned to the global freelist - for this specific bin. This only occurs when a number of blocks - are grabbed from the global list to a thread specific list or when - a thread decides to return some blocks to the global freelist. -</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="allocator.mt.deallocation"></a>Deallocation Notes</h3></div></div></div><p> Notes about deallocation. This allocator does not explicitly -release memory. Because of this, memory debugging programs like -valgrind or purify may notice leaks: sorry about this -inconvenience. Operating systems will reclaim allocated memory at -program termination anyway. If sidestepping this kind of noise is -desired, there are three options: use an allocator, like -<code class="code">new_allocator</code> that releases memory while debugging, use -GLIBCXX_FORCE_NEW to bypass the allocator's internal pools, or use a -custom pool datum that releases resources on destruction. -</p><p> - On systems with the function <code class="code">__cxa_atexit</code>, the -allocator can be forced to free all memory allocated before program -termination with the member function -<code class="code">__pool_type::_M_destroy</code>. However, because this member -function relies on the precise and exactly-conforming ordering of -static destructors, including those of a static local -<code class="code">__pool</code> object, it should not be used, ever, on systems -that don't have the necessary underlying support. In addition, in -practice, forcing deallocation can be tricky, as it requires the -<code class="code">__pool</code> object to be fully-constructed before the object -that uses it is fully constructed. For most (but not all) STL -containers, this works, as an instance of the allocator is constructed -as part of a container's constructor. However, this assumption is -implementation-specific, and subject to change. For an example of a -pool that frees memory, see the following - <a class="link" href="http://gcc.gnu.org/viewcvs/trunk/libstdc++-v3/testsuite/ext/mt_allocator/deallocate_local-6.cc?view=markup" target="_top"> - example.</a> -</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mt_allocator_design.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="mt_allocator.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="mt_allocator_ex_single.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Design Issues </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Single Thread Example</td></tr></table></div></body></html>
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