CODEWITHSUNDEEP
clinuxassemblypthreads
johnfound
johnfound

Reputation: 7061

pthread_mutex_timedlock use from Linux assembly language

The setting:

I am trying to use pthread_mutex_timedlock function from pthreads in my 32 bit assembly language program. The code looks following way:

struct timespec
  .tv_sec  dd ?   ; time in seconds
  .tv_nsec dd ?   ; time is nano seconds
ends

;....
.time timespec  ; the timespec structure
;....
; the code where pthread_mutex_timedlock is used

    mov     eax, [.timeout] ; the timeout in [ms]
    mov     ecx, 1000
    cdq
    div     ecx           ; the timeout in eax [s]
    imul    edx, 1000000  ; the remainder in edx [ns]

    mov     [.time.tv_sec], eax
    mov     [.time.tv_nsec], edx

    lea     eax, [.time]
    cinvoke pthread_mutex_timedlock, [.ptrMutex], eax
    test    eax, eax
    jnz     .error

The problem is that the pthread_mutex_timedlock function locks the mutex only if it is immediately unlocked.

If the mutex is locked in this moment, the function pthread_mutex_timedlock returns immediately with ETIMEDOUT error, without waiting for timeout, ignoring the values set in the timespec structure.

The question:

What I am doing wrong?

Upvotes: 2

Views: 419

Answers (1)

caf
caf

Reputation: 239261

The timeout for pthread_mutex_timedlock() is an absolute timeout, not relative - it's returning immediately because the absolute time represented by your timeout value has passed long ago.

If you want a "timeout in N milliseconds from now" (a relative timeout), you need to get the current time with clock_gettime() (specifying the CLOCK_REALTIME clock, as that's the clock used by pthread_mutex_timedlock()) then offset it by N milliseconds and pass the result to pthread_mutex_timedlock().

Upvotes: 4

Related Questions