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Sets the interrupt request for a target thread.


#include <prthread.h>

PRStatus PR_Interrupt(PRThread *thread);


PR_Interrupt has the following parameter:

The thread whose interrupt request you want to set.


The function returns one of the following values:

  • If the specified thread is currently blocked, PR_SUCCESS.
  • Otherwise, PR_FAILURE.


The purpose of PR_Interrupt is to request that a thread performing some task stop what it is doing and return to some control point. It is assumed that a control point has been mutually arranged between the thread doing the interrupting and the thread being interrupted. When the interrupted thread reaches the prearranged point, it can communicate with its peer to discover the real reason behind the change in plans.

The interrupt request remains in the thread's state until it is delivered exactly once or explicitly canceled. The interrupted thread returns PR_FAILURE (-1) with an error code (see PR_GetError) for blocking operations that return a PRStatus (such as I/O operations, monitor waits, or waiting on a condition). To check whether the thread was interrupted, compare the result of PR_GetError with PR_PENDING_INTERRUPT_ERROR.

PR_Interrupt may itself fail if the target thread is invalid.


PR_Interrupt has the following limitations and known bugs:

  • There can be a delay for a thread to be interrupted from a blocking I/O function. In all NSPR implementations, the maximum delay is at most five seconds. In the pthreads-based implementation on Unix, the maximum delay is 0.1 seconds.
  • File I/O is considered instantaneous, so file I/O functions cannot be interrupted. Unfortunately the standard input, output, and error streams are treated as files by NSPR, so a PR_Read call on PR_STDIN cannot be interrupted even though it may block indefinitely.
  • In the NT implementation, PR_Connect cannot be interrupted.
  • In the NT implementation, a file descriptor is not usable and must be closed after an I/O function on the file descriptor is interrupted. See the memo Using IO Timeout and Interrupt on NT for details.