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relibc_pthreads-emb
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<p style="margin-bottom: 0in;"><big><big><big><span style="font-weight: bold;">PTE on PSP OS</span></big></big></big></p><p style="margin-bottom: 0in;"><br>
</p>
<p style="margin-bottom: 0in;">All PSP OS objects that are created
require a name to be associated with them.  The name must be unique
among objects that currently exist.  To accomplish this, any routines
that allocate OS objects (e.g. <font face="Courier New, monospace">OsMutexCreate</font>)
keep a static local variable that acts as a counter and is
incremented every time an object is created.  This value is appended
to the name of the resource.  For instance &#8220;mutex04&#8221; would be the
name of the fourth mutex created.</p>
<p style="margin-bottom: 0in;"><br>
</p>
<h1 class="western">Thread creation</h1>
<p><font face="Courier New, monospace">OsThreadCreate</font>
allocates a <font face="Courier New, monospace">pspThreadData</font>
structure that contains a semaphore used for cancelling a thread, the
thread's entry point and parameters to the thread's entry point.  A
pointer to this structure is stored as a TLS value.</p>
<p style="margin-bottom: 0in;"><font face="Courier New, monospace">OsThreadCreate</font>
calls <font face="Courier New, monospace">sceKernelCreateThread</font>
with a entry point of <font face="Courier New, monospace">pspStubThreadEntry</font>.
 The stub entry point retrieves the per thread control structure
(allocated during <font face="Courier New, monospace">OsThreadCreate</font>)
and gets the thread's real entry point and parameters and then calls
the real entry point.</p>
<p style="margin-bottom: 0in;"><br>
</p>
<h1 class="western">Thread Local Storage</h1>
<p style="margin-bottom: 0in;">Unfortunately, PSP OS does not include
<b>any</b> kind of thread local storage functionality.  To emulate
TLS, when a new POSIX thread is created, a structure is allocated to
contain TLS keys and values.  A pointer to this structure is appended
to the thread name.  For instance, a new threads name might be 
&#8220;pthread10_80001234&#8221;, where 0x80001234 is the address of the TLS
structure.  When a thread wants to access TLS information, it
retrieves the thread's name from the OS, parses the name to extract
the pointer and then utilizes the TLS helper library to set or get
TLS values. 
</p>
<p style="margin-bottom: 0in;"><br>
</p>
<p style="margin-bottom: 0in;">Unfortunately, this mechanism only
works for threads that are created through pthread_create; it does
not work for OS threads that are using pthread calls.  To emulate
this (at this for one thread) we allocate a single TLS structure
(like the ones associated with each POSIX thread).  This &#8220;global&#8221;
TLS structure is used when pthread is called from a non-POSIX OS
thread.  This introduces the important limitation that pthread calls
can be made from ONLY ONE non-POSIX OS thread.  Behavior when calling
from multiple different non-POSIX OS threads is undefined.</p>
<p style="margin-bottom: 0in;"><br>
</p>
<h1 class="western">Mutexes</h1>
<p style="margin-bottom: 0in;">PSP OS does not supply routines for
mutexes.  A counting semaphore initialized to 0 is used.</p>
<p style="margin-bottom: 0in;"><br>
</p>
<h1 class="western">Thread Cancellation</h1>
<p style="margin-bottom: 0in;">Since PSP OS does not natively provide
a way to break out of blocked operations, this functionality is
emulated using a cancellation semaphore that is stored in the per
thread control data.  When the user requests that a thread be
cancelled (i.e. <font face="Courier New, monospace">OsThreadCancel</font>
is called) this semaphore is posted to.  In
<font face="Courier New, monospace">OsSemaphoreCancellablePend</font>,
the cancellation semaphore as well as the user semaphore are polled
(rather than blocking) and the routine returns if the cancellation
semaphore is posted to.  A similar technique is used for
<font face="Courier New, monospace">OsThreadWaitForEnd</font>.</p>
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