availableConnections | R Documentation |

The number of connections that can be open at the same time in **R** is
*typically* 128, where the first three are occupied by the always open
`stdin()`

, `stdout()`

, and `stderr()`

connections, which leaves 125 slots
available for other types of connections. Connections are used in many
places, e.g. reading and writing to file, downloading URLs, communicating
with parallel **R** processes over a socket connections (e.g.
`parallel::makeCluster()`

and `makeClusterPSOCK()`

), and capturing
standard output via text connections (e.g. `utils::capture.output()`

).

```
availableConnections()
freeConnections()
```

A non-negative integer, or `+Inf`

if the available number of connections
is greater than 16384, which is a limit be set via option
`parallelly.availableConnections.tries`

.

This limit of 128 connections can only be changed by rebuilding **R** from
source. The limited is hardcoded as a

#define NCONNECTIONS 128

in ‘src/main/connections.c’.

Since the limit *might* changed, for instance in custom **R** builds or in
future releases of **R**, we do not want to assume that the limit is 128 for
all **R** installation. Unfortunately, it is not possible to query **R** for what
the limit is.
Instead, `availableConnections()`

infers it from trial-and-error.
until it fails. For efficiency, the result is memoized throughout the
current **R** session.

'WISH: Increase limit of maximum number of open connections (currently 125+3)', 2016-07-09, https://github.com/HenrikBengtsson/Wishlist-for-R/issues/28

`base::showConnections()`

.

```
total <- availableConnections()
message("You can have ", total, " connections open in this R installation")
free <- freeConnections()
message("There are ", free, " connections remaining")
```

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