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doc/go1.2.html: stack sizes, thread limits

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Rob Pike 2013-10-30 08:54:53 -07:00
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@ -137,6 +137,55 @@ This means that any loop that includes a (non-inlined) function call can
be pre-empted, allowing other goroutines to run on the same thread.
</p>
<h3 id="thread_limit">Limit on the number of threads</h3>
<p>
Go 1.2 introduces a configurable limit (default 10,000) to the total number of threads
a single program may have in its address space, to avoid resource starvation
issues in some environments.
Note that goroutines are multiplexed onto threads so this limit does not directly
limit the number of goroutines, only the number that may be simultaneously blocked
in a system call.
In practice, the limit is hard to reach.
</p>
<p>
The new <a href="/pkg/runtime/debug/#SetMaxThreads"><code>SetMaxThreads</code></a> function in the
<a href="/pkg/runtime/debug/"><code>runtime/debug</code></a> package controls the thread count limit.
</p>
<p>
<em>Updating</em>:
Few functions will be affected by the limit, but if a program dies because it hits the
limit, it could be modified to call <code>SetMaxThreads</code> to set a higher count.
Even better would be to refactor the program to need fewer threads, reducing consumption
of kernel resources.
</p>
<h3 id="stack_size">Stack size</h3>
<p>
In Go 1.2, the minimum size of the stack when a goroutine is created has been lifted from 4KB to 8KB.
Many programs were suffering performance problems with the old size, which had a tendency
to introduce expensive stack-segment switching in performance-critical sections.
The new number was determined by empirical testing.
</p>
<p>
At the other end, the new function <a href="/pkg/runtime/debug/#SetMaxStack"><code>SetMaxStack</code></a>
in the <a href="/pkg/runtime/debug"><code>runtime/debug</code></a> package controls
the <em>maximum</em> size of a single goroutine's stack.
The default is 1GB on 64-bit systems and 250MB on 32-bit systems.
Before Go 1.2, it was too easy for a runaway recursion to consume all the memory on a machine.
</p>
<p>
<em>Updating</em>:
The increased minimum stack size may cause programs with many goroutines to use
more memory. There is no workaround, but future plans for future releases
include new stack management technology that should address the problem better.
</p>
<h3 id="cgo_and_cpp">Cgo and C++</h3>
<p>