90 lines
5.2 KiB
HTML
90 lines
5.2 KiB
HTML
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<meta name="DC.Title" content="Thread-private data and thread-specific data" />
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<meta name="abstract" content="Threads cannot share certain resources. Data that threads cannot share between themselves are called thread-private data." />
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<title>Thread-private data and thread-specific data</title>
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<body id="rzahwces-cesco"><a name="rzahwces-cesco"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Thread-private data and thread-specific data</h1>
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<div><p>Threads cannot share certain resources. Data that threads cannot
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share between themselves are called thread-private data.</p>
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<div class="section"><div class="p">The operating system defines this thread-private data. <span class="keyword">i5/OS™</span> defines the following resources
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as thread-private data: <ul><li>Thread identifier:<p>The unique integral number that can be used to identify
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the thread.</p>
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</li>
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<li>Priority:<p><span class="keyword">i5/OS</span> allows
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specification of a thread priority, which determines the relative importance
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of one thread to other threads in the job. The thread priority is defined
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to be a delta value to the job's priority. <span class="keyword">i5/OS</span> adds
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the thread's priority to the job's priority. It can never exceed the job's
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priority. If you adjust the job's priority, the thread's priority is adjusted
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relative to the new job priority. The default thread priority value is zero.
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This results in a thread that has the same priority as the job. </p>
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</li>
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<li>Security information:<p>Security information, including user and group
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profiles, is maintained on a per thread basis. When a thread creates a new
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thread, the new thread inherits the security information from the thread that
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created it.</p>
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</li>
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<li>Library list:<p>Library list information, including user and group profiles,
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is maintained on a per thread basis. When a thread create a new thread, the
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new thread inherits the library list information from the thread that created
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it.</p>
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</li>
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<li>Signal blocking mask:<p>The signal blocking mask identifies the set of
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asynchronous signals to be blocked from delivery to the thread. When a thread
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creates a new thread, the new thread inherits the signal blocking mask of
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the thread that created it. </p>
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</li>
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<li>Call stack:<p>The call stack contains data about the program flow or procedure
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call flow in a thread. The stack, along with automatic storage, is allocated
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for each thread created.</p>
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</li>
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<li>Automatic storage:<p>Automatic storage is for variables that are local
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to the function. </p>
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</li>
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<li>errno variable:<p>The program variable that is used to return the result
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of a C or POSIX system call. errno is a function call that returns the most
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recent result for a function call in the thread.</p>
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</li>
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</ul>
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</div>
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<p>Threads can have their own view of data items called thread-specific
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data. Thread-specific data is different from thread-private data. The threads
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implementation defines the thread-private data, while the application defines
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the thread-specific data. Threads do not share thread-specific storage (it
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is specific to a thread), but all functions within that thread can access
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it. Typically, a key indexes thread-specific storage. The key
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is a global value that is visible to all threads. It is used to retrieve the
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thread-specific value of the storage associated with that key.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwas4co.htm" title="All programs have at least one thread, referred to as the initial thread. In a program with multiple threads, each thread runs its code independently of the other threads in the program.">Threads on i5/OS</a></div>
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</div>
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</div>
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</body>
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