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## nng_cv_wait
Wait for condition.
### Synopsis
```c
#include <nng/nng.h>
#include <nng/supplemental/util/platform.h>
void nng_cv_wait(nng_cv *cv);
```
### Description
The `nng_cv_wait` waits for the condition variable _cv_ to be signaled
by another thread calling either xref:nng_cv_wake.adoc[`nng_cv_wake`] or
xref:nng_cv_wake1.adoc[`nng_cv_wake1`].
The caller must have have ownership of the mutex that was used when _cv_ was allocated.
This function will drop the ownership of that mutex, and reacquire it atomically just before returning to the caller.
NOTE: Any condition may be used or checked, but the condition must be checked, as it is possible for this function to wake up spuriously.
The idiomatic way to do this is inside a loop that repeats until the condition is true.
### Example
The following example demonstrates use of this function:
.Example 1: Waiting for the condition
```c
nng_mtx_lock(m); // assume cv was allocated using m
while (!condition_true) {
nng_cv_wait(cv);
}
// condition_true is true
nng_mtx_unlock(m);
```
.Example 2: Signaling the condition
```c
nng_mtx_lock(m);
condition_true = true;
nng_cv_wake(cv);
nng_mtx_unlock(m);
```
### See Also
xref:nng_cv_until.adoc[nng_cv_until],
xref:nng_cv_wake.adoc[nng_cv_wake],
xref:nng_cv_wake1.adoc[nng_cv_wake1],
xref:nng_mtx_lock.adoc[nng_mtx_lock]
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