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The DbEnv Handle
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< h2 class = "title" style = "clear: both" > < a id = "envset_thread_count" > < / a > DbEnv::set_thread_count()< / h2 >
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< pre class = "programlisting" > #include < db_cxx.h>
int
DbEnv::set_thread_count(u_int32_t count); < / pre >
< p >
Declare an approximate number of threads in the database
environment. This method allocates resources in your environment
for the threads your application will use. If you fail to properly
estimate the number of threads your application will use, your
application will run out of resources and errors will be returned
when the application attempts to start one too many threads.
< / p >
< p >
The < code class = "methodname" > DbEnv::set_thread_count()< / code > method does not set the
maximum number of threads but is used to determine memory sizing and
the thread control block reclamation policy.
< / p >
< p >
The < code class = "methodname" > DbEnv::set_thread_count()< / code > method must be called
prior to opening the database environment. In addition, this method must be
used with the
< a class = "xref" href = "envfailchk.html" title = "DbEnv::failchk()" > DbEnv::failchk()< / a > method.
< / p >
< p >
If a process invokes this method without the use of
< a class = "xref" href = "envfailchk.html" title = "DbEnv::failchk()" > DbEnv::failchk()< / a >
the program may be unable to allocate a thread
control block. This is true of the standalone Berkeley DB utility
programs.
< / p >
< p >
If a process has not configured an < span class = "bold" > < strong > is_alive< / strong > < / span > function from the
< a class = "xref" href = "envset_isalive.html" title = "DbEnv::set_isalive()" > DbEnv::set_isalive()< / a >
method, and then attempts to join a database environment configured
for failure checking with the < a class = "xref" href = "envfailchk.html" title = "DbEnv::failchk()" > DbEnv::failchk()< / a > ,
< a class = "xref" href = "envset_thread_id.html" title = "DbEnv::set_thread_id()" > DbEnv::set_thread_id()< / a > ,
< a class = "xref" href = "envset_isalive.html" title = "DbEnv::set_isalive()" > DbEnv::set_isalive()< / a > and
< code class = "methodname" > DbEnv::set_thread_count()< / code > methods, the program may be unable to
allocate a thread control block and fail to join the environment.
< span class = "bold" > < strong > This is true of the standalone Berkeley DB
utility programs.< / strong > < / span > To avoid problems when using the
standalone Berkeley DB utility programs with environments configured
for failure checking, incorporate the utility's functionality directly
in the application, or call the
< a class = "xref" href = "envfailchk.html" title = "DbEnv::failchk()" > DbEnv::failchk()< / a > method
before running the utility.
< / p >
< p >
The database environment's thread count may also be configured
using the environment's < a href = "../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class = "olink" > DB_CONFIG< / a > file. The syntax of the entry
in that file is a single line with the string "set_thread_count",
one or more whitespace characters, and the thread count. Because
the < a href = "../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class = "olink" > DB_CONFIG< / a > file is read when the database environment is
opened, it will silently overrule configuration done before that
time.
< / p >
< p >
The < code class = "methodname" > DbEnv::set_thread_count()< / code > method configures operations performed
using the specified < a class = "link" href = "env.html" title = "Chapter > DbEnv< / a > handle, not all
operations performed on the underlying database environment.
< / p >
< p >
The < code class = "methodname" > DbEnv::set_thread_count()< / code > method may not be called after the
< a class = "xref" href = "envopen.html" title = "DbEnv::open()" > DbEnv::open()< / a > method is
called.
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< p >
The < code class = "methodname" > DbEnv::set_thread_count()< / code > < span >
< span >
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
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< / span >
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< h3 class = "title" > < a id = "id3607074" > < / a > Parameters< / h3 >
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< h4 class = "title" > < a id = "id3607080" > < / a > count< / h4 >
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The < span class = "bold" > < strong > count< / strong > < / span > parameter is an approximate
thread count for the database environment.
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< h3 class = "title" > < a id = "id3606905" > < / a > Errors< / h3 >
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The < code class = "methodname" > DbEnv::set_thread_count()< / code > < span >
< span >
method may fail and throw a < a class = "link" href = "dbexception.html" title = "Chapter > DbException< / a >
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
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< h4 class = "title" > < a id = "id3607298" > < / a > EINVAL< / h4 >
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If the method was called after < a class = "xref" href = "envopen.html" title = "DbEnv::open()" > DbEnv::open()< / a >
was called; or if an invalid flag value or parameter was specified.
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< h3 class = "title" > < a id = "id3606977" > < / a > See Also< / h3 >
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< a class = "xref" href = "env.html#envlist" title = "Database Environments and Related Methods" > Database Environments and Related Methods< / a >
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