7
Currently (Oct 10, 1996) NSPR 2.0 has two modes. Either _PR_NTHREAD
8
is defined, in which case the PR_CreateThread() call always creates a
9
native kernel thread, or _PR_NTHREAD is not defined and PR_CreateThread()
10
always creates user level threads within the single, original process. This
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source code is reflected in two directories, nspr20/pr/src/threads/native, and
12
nspr20/pr/src/threads/user. Although the PR_CreateThread() function has
13
a paramter to specify the "scope" of a thread, this parameter is not yet
14
used- except on solaris where it uses it to specify bound vs unbound threads.
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The next step is to provide a combination of user and native threads. The
19
idea, of course, is to have some small number of native threads and each of
20
those threads be able to run user level threads. The number of native
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threads created will most likely be proportional to the number of CPUs in
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the system. For this reason, the specific set of native threads which are
23
used to run the user-level threads will be called "CPU" threads.
25
The user level threads which will be run on the CPU threads are able to
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run on any of the CPU threads available, and over the course of a user-level
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thread's lifetime, it may drift from one CPU thread to another. All
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user-level threads will compete for processing time via a single run queue.
30
Creation of a CPU thread will be primarily controlled by NSPR itself or by
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the user running a function PR_Concurrency(). The details of PR_Concurrency()
32
have not yet been worked out; but the idea is that the user can specify to
33
NSPR how many CPU threads are desired.
35
In this system, user-level threads are created by using PR_CreateThread() and
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specifying the PR_LOCAL_SCOPE option. LOCAL_SCOPE indicates that the thread
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will be under the control of the "local" scheduler. Creating threads with
38
GLOBAL_SCOPE, on the other hand will create a thread which is under the
39
control of the system's scheduler. In otherwords, this creates a native thread
40
which is not a CPU thread; it runs a single thread task and never has more
41
than one task to run. LOCAL_SCOPE is much like creating a Solaris unbound
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thread, while GLOBAL_SCOPE is similar to creating a Solaris bound thread.
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To implement this architecture, the source code will still maintain the "user"
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and "native" directories which is has today. However a third directory
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"combined" will also exist. To compile a version of NSPR which only creates
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native threads, the user can define _PR_NTHREAD. For exclusive user-level
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threads, do not define _PR_NTHREAD. To get the combined threads, define
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_PR_NTHREAD and _PR_USE_CPUS.
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Phase 3 - later than next week
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The goal is to eliminate the 3 directories. Once these three models are in
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place, the remaining work will be to eliminate the native and user thread
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directories for all platforms, so that the entire thread model is contained
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within what is today called the "combined" model. This new and glorious
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source code will attempt to make the "combined" model on any platforms which
59
provide the necessary underlying native threading, but will also be
60
capable of using exclusive user-level threads on systems which don't have