This call suspends the current thread for a specified time. If the requested interval is 0, the call gives up the remainder of the current time slice.


DosSleep (TimeInterval)

  • TimeInterval (ULONG) - input : Time interval in milliseconds until the thread is awakened.
Return Code

rc (USHORT) - return Return code descriptions are:

  • 0 NO_ERROR

DosSleep suspends the current thread for the specified time period. The actual time it is asleep may be off by a clock tick or two, depending on the execution status of other threads running in the system.

If the time is 0, the thread gives up the remainder of the current time slice and allows any other ready threads of equal priority to run with the current thread for its next slice. Because the amount of sleep time specified is 0, an immediate return with 0 delay is made if no other ready thread is found. However, DosSleep does not yield to a thread of lower priority.

If the time is non-0, the time is rounded up to the resolution of the scheduler clock.

If DosSleep is used to regularly poll an external source to determine the occurrence of some event, a time equal to the longest response interval should be used.

For short time intervals, the rounding-up process combined with the thread priority interactions may cause a sleeping interval to be longer than requested. Also, when a process completes sleeping, it is scheduled for execution. But that execution could be delayed by hardware interrupts or by another thread running at a higher priority. A program should not use the DosSleep call as a substitute for a real-time clock because rounding of the sleep interval causes cumulative errors.

Asynchronous timers can be started with DosTimerAsync and DosTimerStart. DosTimerAsync starts a one-shot asynchronous timer, and DosTimerStart starts a periodic interval timer. DosTimerStop is issued to stop these timers.

Note: To ensure optimum performance, you should not use DosSleep in a single-thread Presentation Manager application. See WinStartTimer.

Family API Considerations

Some options operate differently in the DOS mode than in OS/2 mode. Therefore, the following restrictions apply to DosSleep when coding in DOS mode:

  • DosSleep accuracy can be in error by 0.5%.
  • DosSleep can degrade system performance of non-foreground program operations when DOS mode is in foreground.
Example Code

C Binding


USHORT  rc = DosSleep(TimeInterval);

ULONG            TimeInterval;  /* Interval size (in milliseconds) */

USHORT           rc;            /* return code */

The following example illustrates how to obtain the priority of a thread and how to change the priority. The main thread creates Thread2 and allows it to begin executing. Thread2 iterates through a loop that prints a line and then sleeps, relinquishing its time slice to the main thread. After one or two iterations by Thread2, the main thread obtains Thread2's priority information and prints it. It then raises Thread2's priority to fixed-high, and increments the level by ten. Since Thread2 is now at a high priority, it immediately finishes its remaining iterations before relinquishing control on a long sleep; at this point, the main thread re-examines Thread2's priority and reports its new priority level. In this example, it is helpful to understand how the DosSleep calls are used either to relinquish control of the processor, or to keep a thread alive (see DosTimerAsync or DosTimerStart for alternatives to DosSleep).


#include <os2.h>

#define    PRTYC_FIXEDHIGH   4      /* Priority class: fixed-high */
#define    PRTY_DELTA        10     /* Priority delta: increase by 10 */
#define    SEGSIZE           4000   /* Number of bytes requested in segment */
#define    ALLOCFLAGS        0      /* Segment allocation flags - no sharing */
#define    SLEEPSHORT        0L     /* Sleep interval - 5 milliseconds */
#define    SLEEPLONG         20L    /* Sleep interval - 75 milliseconds */
#define    RETURN_CODE       0      /* Return code for DosExit() */

  USHORT     i;

  /* Loop with four iterations */
  for(i=1; i<5; i++)
    printf("In Thread2, i is now %d\n", i);

    /** Sleep to relinquish time slice to main thread **/
    DosSleep(SLEEPSHORT);          /* Sleep interval */
  DosExit(EXIT_THREAD,             /* Action code - end a thread */
          RETURN_CODE);            /* Return code */

  USHORT     Priority;            /* Thread priority */
  USHORT     Class;               /* Priority class */
  USHORT     Level;               /* Priority level */
  SEL        ThreadStackSel;      /* Segment selector for thread stack */
  PBYTE      StackEnd;            /* Ptr. to end of thread stack */
  USHORT     rc;

  /* Allocate segment for thread stack; this is better than just */
  /* declaring an array of bytes to use as a stack.  Make pointer eos. */
  rc = DosAllocSeg(SEGSIZE,                    /* Number of bytes requested */
                   &ThreadStackSel,            /* Segment selector
                                                       (returned) */
                   ALLOCFLAGS);                /* Allocation flags */
  StackEnd = MAKEP(ThreadStackSel, SEGSIZE-1);

  /* Start Thread2 */
  if(!(DosCreateThread((PFNTHREAD) Thread2,    /* Thread address */
                       &ThreadID,              /* Thread ID (returned) */
                       StackEnd)))             /* End of thread stack */
    printf("Thread2 created.\n");

  /** Sleep to allow Thread2 to execute **/
  if(!(DosSleep(SLEEPLONG)))                       /* Sleep interval */
    printf("Slept a little to let Thread2 execute.\n");

  /** Obtain Thread2's priority information and report it **/
  if(!(rc=DosGetPrty(PRTYS_THREAD,                /* Scope - single
                                                         thread */
                     &Priority,                   /* Address to put
                                                          priority */
                     ThreadID)))                  /* ID - thread ID */
    /* Extract priority class and level information */
    Class = HIBYTE(Priority);
    Level = LOBYTE(Priority);
    printf("Thread2: ID is %d, Priority Class is %d and Level is %d\n",
           ThreadID, Class, Level);
  /** Raise Thread2's priority **/
  if(!(rc=DosSetPrty(PRTYS_THREAD,             /* Scope - single thread */
                     PRTYC_FIXEDHIGH,          /* Prty class - fixed-high */
                     PRTY_DELTA,               /* Prty delta - increase
                                                      by 10 */
                     ThreadID)))               /* ID - thread ID */
    /* Obtain Thread2' new priority information and report it */
    rc=DosGetPrty(PRTYS_THREAD,                /* Scope - single thread */
                  &Priority,                   /* Address to put
                                                       priority */
                  ThreadID);                   /* ID - thread ID */

    /* Extract priority class and level information */
    Class = HIBYTE(Priority);
    Level = LOBYTE(Priority);
    printf("Thread2: ID is %d, New Priority Class is %d and Level is %d\n",
           ThreadID, Class, Level);

MASM Binding


PUSH   DWORD   TimeInterval  ;Interval size (in milliseconds)
CALL   DosSleep

Returns WORD


en/docs/fapi/dossleep.txt · Last modified: 2018/08/26 09:04 by prokushev